I gotta fight this kid at school I need help, how can i get out of it?

Blow him off, but if he decides to fight you and he throws the first punch just give him one firm slap across the throat (not as hard as you can, more like about 2/3 to 3/4 strength). Trust me, he'll go down. The important thing is he has to hit you first. That way you can claim self-defense.