MattB,
Zac has a solid point here. Honestly though, I don't think you need to just give up then and there. If the girl doesn't respond, give her a day of radio silence (don't contact her), then try again. The next time you get her out though, you really ought to persist because if you did the last time, she would have eventually given in! The thing is, now that it's the second date, it's going to be a lot harder to have sex with her, but it's still possible! Get her out and be persistent and hope for the best! If you've got an abundance of girls around, then I wouldn't bother, but if she's the only girl you're seeing or 1 of a few then I suggest take the shot! Even if it fails miserably you'll gain more knowledge to use for next time!
Cheers,
Garrett