I Have Been Slapped Across The Face

Well opposing to my usual over the top long stories, this is gonna be a short one. I got slapped in the face today. Not by my ex or an attacker. But by a student in my class room. I should start by saying I'm a 10 th grade teacher and tend to be very kind to every one. But today I was having one of those bad days that got me really in to a bitchy mood. Long storie short I ended up hitting a student in my classroom over the back. And as a response he slapped my face twice which got me and my class dumb struck. And then he threatened to sue me in court. I just left him alone and took the rest of the day off. And now hear that this has turned in to a hot topic. I'm too afraid to call his parents because I might lose my job. So I disided to apologize to him first thing tomorrow. What do you guys think I should or should've done?