First off, I think your mom is great! Giving you a gift that can help you
get around and get fit. I agree w/ Mr. Beanz that you should find out if
this bike fits you. What's your inseam/height and what size is the bike?
It may be possible to exchange it if it's not the right size. Tires will always
give/fatten a bit when you mount a bike, I ride on 120 PSI tires and I can
see them squish when I mount my roadbike. Once you get the size sorted
out, just go out and ride. Don't worry you won't damage that bike just
spinning around the neighborhood