i think you should stretch all your major mucscles after class, if you can, and hold everything for thirty seconds. muscles will lengthen in time. dont push it.
you can also warm up at home. go ahead and do your regular ballet warmup if you know it well enough or turn on some music and make one up. then stretch. it will feel better too.
of course, i am 15 and just starting too, so this is just based on what i know of now.[/i]