I remember a similar situation happening to me when I was a young man. Walking around with a hard-on all day at the thought of being with her only to loose it when our clothes came off. I was shocked and confused because it had never happened to me before and she questioned if I was attracted to her or not. When we tried again everything worked as it should, so I wouldn't worry about it.
Best of luck and enjoy :)

And now you have the rest of the story.

So, it personally took me several times of my girlfriend going down on me before I ever finnished, probably for the same reason you couldn't get it up. But as soon as it happens once, it's never a real issue again (at least it wasn't in my case). Don't worry, I'm sure she'll give you annother chance, just explain that you were really nervous.

It was almost certainly just nerves - don't worry. Next time just concentrate on how good it feels. You could also reciprocate (69) or something else to make her feel good, so you don't focus on getting hard. Get your mind off of it and I practically guarantee the little guy will perk right up.

ummm tell the chick that we need to try that again.

If it fucks up that time dump her and tell all you friends she's terrible at head before she tells hers you can't get it up :D