Would you consider this sexist?

Yes, you are completely right. With our class, all the boys and girls do the exact same, except one time we got to play basketball because the girls had to go into the gym for testing, but it was opted that way because the girls didn't want to be around guys because we were testing weight and height, which is understandable. If it's coed P.E that means you are taught TOGETHER and right now you're being segregated because of who you are, which is not allowed. I would first talk to your parents about this, see what they have to say, and then take it farther i.e the P.E teacher and the principal. I don't think this is fair, so go talk to them bout it