Do you think she's overreacting?

Okay so here's the story, Two nights ago I remembered It was going to be my girlfriends Birthday( 1year 3 months ^-^) the day after, but I had no money to get her anything, so I call my friend to give me any ideas that would get me cash fast, he brought up his little fight club he had going on but I had refused many times before, But this time I had no other choice but to do it. He told me the last man standing wins 3 grand, so I figure might as well give it a try, So I go, and i actually win ( im not going to lie they hurt me pretty bad but I say it was worth it :D ) So with my newly hard earned cash I decided to buy her a diamond necklace, On my way there, I looked at my reflection and I was cut up pretty bad and I had a Black eye, I couldn't really do anything about it since the store was going to close, so i went in there and purchased the necklace and left, I got home and tried to put the swelling down and disinfected my cuts. The next day I arrived at her home, But she was shocked to see me in that state and asked me what happened, Of course i wasnt going to tell her, but she called my buddy and his dumbass didn't know she was going to flip out if she actually knew what I did to get her that necklace. Now she knows and shes pretty pissed at me, she doesn't even want to talk, what should I do to calm her down? Why is she so mad? any ideas?