u go girl
as for the teacher rushing into it.... so so wrong, i kno for a fact that when u are taught how to teach things like that. the class should be split into sections, warm up, main body of class, and cool down, each with their own group of exercises, sometimes even different music.... i kno my boss has specific aerobic cd's with music that changes BPM at certain times to allow for the cool down section after the class
i am guessing this is for an aerobics class as well claire?
great warm up for a class is the x-trainer, or even the rower, 5 mins on either one of those, gradually building up the speed works well mainly cause you are using virtually all your major muscle groups
then have a think about what is happenin in the class and do some stretching / go through range of motion of the muscles bein used, quads, hamstrings, calves, adductors, will all be used a lot in a step / aerobics class, holding each stretch for 15 seconds on each leg.... should get your heart rate up and muscles nicely warm before hand.
if you want to be pointed in the direction of some decent stretches let me know