Hi,
I can understand that you don’t like sitting in class because sometimes I also think like you! Nevertheless, I have to respond to you very carefully because I don’t want to disturb your studies. What is the major reason why you don’t like sitting in class? This reason would be key to solve your problem. If you can’t find the reason, then I suggest you to ask your teacher and to say “Can I stand up during the class” or “Can I go to the bathroom.” The second phrase is one of my favorite excuses when I don’t like sitting in class, but please don’t use it too much because it can be rude for your teacher.
We always support your opinion for your best.