I really think I'm going to freak out at my stepdad.
Why would you freak out at your stepdad? Did he do something wrong?
I've tried to stay calm but he's a total asshole.
It's not nice to freak out at your step-parents. You need to learn to be a little more calm in your approach.
He treats me like shit. There is no other way around it.
You can't be expected to always get along with your stepdad and your complaints are probably valid, but I don't think freaking out is the solution. Try talking to him calmly as he'll probably be more receptive to your feels and problems you are having with his behavior.