I messed up with my bf. Help!!!?

Me and my now ex have been together for a year on and off and for the past couple of weeks we have been trying to get back together I guess u could say. Kinda a trial to see if he could fix his problems and not be such a jerk. Well the other day one of my guy friends I've known since kindergarten had a extra ticket to rodeo and to go with his parents and I said yeh I would go. But when I asked my "bf" he said no. Well me being stupid I went behind my bfs back and went anyway. And I lied to him about it and told him I was grounded for the day. Well as the day went on he started getting suspious to why I wasn't texting him back or answering his calls. So I told him the truth. Well now he's saying screw u. I want nothing to do with u. How do I fix this??? I know I messed up. And plz no stupid comments