I'm trying to update my wardrobe and found some Levi's that don't gap in the back like so many jeans do on me. I was excited about having a pair of dark wash jeans, finally, and they fit like a glove. That is, until I wore them for a few hours. Now they're baggy and not as fashionable.

They're 1% elastane and 99% cotton. Should I try washing them on hot and putting them in a hot dryer? Or would that wreck them/shorten them? In the future should I buy down a size, to something that's uncomfortably tight at first?