Nervous over my larger boat purchase. Is this normal?

Not the only one and not the only one to overestimate the difficulty. A well behaved larger boat often maneuvers better than a smaller one. The weight actually makes it easier in many cases and less moved by current and wind. Any two boats are different, but I wouldn't think of the 45 as more difficult than your 36.

The bigger the boat the easier it is to handle as it won’t get blown away like smaller and lighter boats

I remember some 20 years when i jumped from a 37 express to my 53 Hatteras MY. First few minutes it was like... oh s—t this is big what did I get myself into. Later that day it became... wow this is a lot easier than the smaller boat.

you ll get over it. Very quickly.

two things to remember. First the thrusters if electric can only be used for a limited time before they run hot and shut down. Second, you can’t manhandle a larger boat into a dock and you or your crew can’t do acrobatic like jumping on the dock to secure the boat. All line handling is done from the boat

of and make that three things. Number three being spring lines are you best friends.

Had the same feeling when I was very much used to my 33’ sailboat, then took a job operating a private Johnson 70.
Got a quickie checkout by another Captain, then solo..
Got used to it somehow, but not coming back to the slip at Bahia Mar, getting the boat in position, then run down to the aft deck from the fly bridge, activate the controls and backing her in without seeing much forward or the other side. It had 25hp bow and stern thrusters, easy enough to maneuver, but I always had a Mate, or the owner was helping.
Prefer boats I can operate safely solo, but they don’t pay as much.

I remember when one client I taught to run his single I/O called for another lesson when he bought his first twin. He was all nervous. I laughed as I told him his life just got a whole lot easier. Same thing as you get bigger. It's less affected by wind and current. Add to that the bow and stern thrusters and I say Sleep well tonight. You're going to enjoy your new boat. Congratulations and welcome to YF.

Rick... went from a 20'I/O to my 56' Neptunus. Sure the first few trips from and into the dock were very slow had the pucker factor. Now, I'm just very cautious and slow and my heartbeat only speeds up a little.
You'll be fine

When I see these jockeys who slam their boats into their slips it looks cool. To me it just tells me that's someone who never had a gear linkage come lose or break. I always tried to impress on people I taught that Slow is Cheap.

There is no doubt that a larger boat is less affected by wind but I don’t think boat size makes a difference when it comes to current. Current affects any that floats the same way whether a 100 footer or a kayak.

Once an item is moving you're correct, but it takes more effort and time to get things moving the heavier they. A cruise ship is a lot less affected by a 5 kt. current that a Boston Whaler.
P.S. What's the difference between an air current and a water current? Resistance.

According to a book I read on boat handling, by some US Navy Admiral, the current is 5 times stronger than the wind.
(5 knots current is the same as 25 knots of winds)
Great book by the way, highly recommended, how to maneuver subs in narrow channels and other goodies.

Again resistance. In that case by the density of the medium.

Of course you aren't.
But as already said, in most cases (yours included, I believe) the change actually brings an improvement in maneuverability.
Just a matter of getting used to the boat reactions and dimensions.

The only thing which is bound to get worse with size/weight is the risk of damages.
It's a simple matter of physics: more mass, more inertia, less chances for any given area of fiberglass/gelcoat to withstand an impact.
So, worth bearing in mind what NYCAP suggested: slow is cheap.

For the same reason, don't forget to tell your crew (which might have been used to that with the smaller boat) that trying to avoid an impact with hands and arms is never a good idea.
If worse comes to worst, better pay some boat yard work, rather than a doctor!

This is important. The engine & thrusters are stronger than the crew and you will learn to use them effectively. Fingers don't grow back.

And Congratulations too

And a rigid rule that no one does anything, no guest tries to help, unless instructed to by the captain. In fact, our rule is that they stay seated in place unless asked. Most of those on board in our case, know what they're doing and know how to help but can't have everyone moving around and getting involved.

That drives me nuts.... when guests try to “help” without asking or even when they ask. Usually the question includes “I am a boater, I have a ——-“ almost always under 40’.

The other rule I never want to see being broken on board is nobody gets on the swimplatform to handle lines. Never. Ever. Access gates are closed and lines get handled from the deck behind the rail. I don’t care if the boat has nice stairs going down, a 10’ swimplatform and even staples type rails along the stern. If the sides of the platform are open nobody goes there till engines are off. I have seen too many experienced crew fall in the drink while line handling without rails

I find a good skipper's command when maneuvering/docking/anchoring and so forth is "stand by".
I use this whenever a spare hand on board or on the dock asks if assistance is needed.
Sounds better than "no", and who knows, I may need assistance.
So "stand by".

This will avoid when a well minded hand pulls the bow in just when you wanted to keep your stern where is was.

You should be fine going from a Monk 36 to 45 Symbol.

Only go as fast as you are willing to hit something

Neutral is my friend

I find "stand by' a bit ambiguous and nautical unless dealing with a deck or dock hand I intend to use shortly, and I'd keep one eye on them after that. I prefer to be more direct, which once came to "Drop that f------g line" when a dock hand wanted to debate if he should drop a line that was keeping me from getting out of a bad situation. 'Take this' 'Do that' as short and plain as it can be work better. I'll tender apologies after the boat is on the dock if they're offended. Right now is when directives need to be followed on a boat. My wife's cousin was sailing with her husband through a gale once and he told her to release a sail Her response was 'let me get the coffee first' as she headed below.

There is more to it than Stand By to be sure.
While I know it is not always the case, I find many folks at marinas are a bit nautical.

Unless we trust the dock hands, like at Staniel Cay, we handle our own lines and secure the boat from the deck. Same when leaving. All lines are doubled up and released in the proper sequence from the boat

I have seen some people getting offended when we tell them we don’t need help but tough s....

I DK about that. I remember my boss on one boat was always intrigued by my words and expressions as he tried to figure them out and learn nautical speak. One day I said "Check out the Russian sub". After a few minutes he said "Ok I give up. What's a Russian sub". to which I replied "That boat over there with the red star on the conning tower". I've known a lot of "boaters" who knew little more than how to mix a martini. I wouldn't want them guessing what I mean.