Hmm, maybe the busdriver will sit down and eat his lunch if it takes you that long, but somehow I doubt it to such an extend I am willing to put a bet on it.
No seriously; I find getting anything with wheels on the bus so much easier than parallel parking a car. When I first got my
ECV years ago (hear granny talk.........) I had to stall it in the main hall. Well, that was a place with some big stairs in it and I would have to drive past the stairs and make a 90 degree turn. Mind you; it was just about wide enough to fit the ECV, get off it and make the turn with about 1 inch left on both sides. So more or less; make the turn right the first time or find yourself struggling. It took me a whopping 2 tries to get the hang of making that turn and never had any problems with it again. Parallel parking? Well, let me just say I was glad I pulled it of for the first time during my exam (got better at it later, but needed more practice than the ECV).
One thing that might help you is to try and allways be the one to board first. Not just before those walking, but the first ECV and/or wheelchair. (of course if there is nobody on the bus yet in one...) In those situations you will have 2 spots vacant, so you'll have more room to make your turns.
Also you might find it beneficial to see if you prefer to parallel park backing up or straigth forward. On some busses you can do both, depending a bit on the type of ECV and it's possibilities.
And if all fails; just listen to the busdriver. They tend to know enough of the basics to give you just the right directions to get in without totally tearing the bus apart. (allthough I tend to be a hand full, I always do it in my own way -read; something else than what most drivers are used to, which means some break out in a sweat-attack fearfull of me ripping their beloved bus to pieces-)
PS; you simply CAN NOT, I repeat CAN NOT know your limits on a subject you've never tried. It's your first ECV-in-Disney-bus trip, so untill proven otherwise I refuse to believe you can't get the hang of getting the ECV on the bus.