Will you have the capability to bail out? I've started centuries with what I felt to be inadequate training. My wife has been ready to come rescue me with the van if I called.

45 miles is a lot for a non-rider. I took a group of people on a bike ride into town to go to the movies. It was 12 miles. Several of them complained about sore butts, and some were noticably fatigued, especially going up hills towards the end. (None of them was guilty of much exercise in their regular routines, but none were obese either.)

45 miles is a long ride for me these days because I can only squeeze a ride in once a week, and usually around 25 miles. If I went out and rode 45 I'd be pooped at the end. I'd make it fine, but would be pooped. If you haven't been riding at all you may end up more than pooped.

If you go, take lots of breaks. It's amazing how rejuvenating a half-hour rest can be. Don't try to keep up with your faster friends.

Consider having someone to come rescue you. It's not a badge of dishonor, it's discretion being the better part of valor. Go as far as you can. Maybe you'll make it all the way, but if it's obvious you're not going to you'll have a way out.

Good luck.