Well I doubt fighting the kid would have helped looking at the outcome for just pushing him!
You get a gun pointed at you for pushing, what do you get for kicking the crap (or attempting) out of him? Maybe the trigger gets pulled? They find where you live and target not only you but your family?
Smart move!
Running away was the best option.
Just call the police like someone else said, and get it sorted. I personally recommend not going to school tomorrow. What did your parents say?!