What should I do?!

Okay, so my parents always force me to go to stupid karate but I don`t want to. I never wanted to. I think it`s a waste of my time and I always have school projects and stuff like that to work on. Every time I try and tell her that I don`t want to go, and even when I list my reasons why, she never listens. She even punishes me for saying I don`t want to do it. Even a long time ago, my parents asked me and my other two siblings if we still wanted to do karate, and I was the only one who said no. And, sometimes my projects are so big that I stay home from doing fun stuff, like going to the pool and stuff like that just to finish my project and she still tries to force me to do karate. Please help!