Dear noxitb,
Unfortunately you just admitted you broke school rules (I assume your school says that any form of violence including hitting someone back is a breach) and school has a wide range of options - punish all of you, one of you, or none of you. I am not aware of any concept of self defence in a school context either. It is unclear from your post if there is anything legally that would help you.
Good luck!
-Nighthelyn