Tried to lose virginity, but couldn't get hard

I was planning on losing my virginity the other night, but it didn't happen. It was with a girl that I've known for a while, and normally I am not really sexually attracted to her. The girl and I were both quite drunk that night, though-we had been drinking liquor and mixed drinks over the course of 4 or 5 hours. We were making out for a little while at the bar, and made out some more when we got back home, and I got hard when we were making out. As soon as we laid down and started fooling around, I realized that I couldn't get an erection. I became embarrassed, and didn't even really want to take my boxers off because I couldn't get hard. I was irritated and embarrassed, especially because I wanted to have sex for the first time, but I realize that this may be a blessing that I didn't make a mistake and lose it with this girl. What could have caused this? Lack of physical attraction, alcohol consumption, nerves? I have some anxiety problems that are normally under control, but now I've been worrying that this will keep happening next time, and it's all I've been thinking about. I don't want to continue this and make it an ongoing problem. Help! What's wrong?

PS I never have a problem getting hard when I'm by myself.