So I Pranked My Teacher Today

I put gum in my math teacher’s chair. Yeah, I know, petty right? She gave me a detention for being late last week and now she walks around with this permanent frown. So today, before first period, I stuck some gum under her seat while the room was empty. Now everyone's trying to act like they didn't see me looking guilty as I walked away. Is it bad that I laughed inside when she sat down? Should I tell on myself and get detention for a joke or is this my way of leveling the playing field? What would you do? Am I just being a kid?