My opinion:
If this girl is the first girl you've become sexually active with, I'd consider it normal. Until you get used to the feeling that go along with sex, I'd expect someone to prematurely shoot their load. I'll admit I was the same way when flygirl and I first started having sex.
And I totally agree with the others, choke the chicken before you go and see he if you expect to get your freak on so that you'll last longer. Also, if she's cool about it she'll understand it and work with you to help you relax.
Basically, just go with the flow.
