I asked a girl to prom, but a week after I asker her, she got a boyfriend. What the hell should I do?

I asked a girl to prom. She said yes, so that week we got the bid for prom. She got a dress, and I got the tux to match the dress. That weekend, she got a boyfriend, and he is planning to go to prom. But she is still going with me to prom. I just don't know whats going to happen when I'm there. Can you give me some advice, or help on what i should do?