Why my legs hurt!

So I've been back to ballet class for about four months now...feeling pretty confident and some-what in shape...and then I had to go and do this to myself! I did this 50-minute workout for the first time this morning and WOW...it was awesome! I am already getting sore, which makes me really nervous for how I will feel when I wake up tomorrow! I would highly recommend this to anyone who has a little ballet experience...but get ready to have your lower body worked over! btw this is on sale at Amazon for only $6.99 right now