Yay- see you're getting much faster!!!! Woo hoo!!
New tires also make a difference. When I got new tires on my bike and had to change a flat- they were hard as heck to get back on (and I could change my old tires in less than 3-4 min). New tires are always so much tighter and more difficult to get back on. Maybe it's the tires, and not you!

Have fun at your class!!!