If the mood is set and she's almost waiting for you to kiss her, then don't let her down. However, never ever ask a girl if you can kiss her, especially on the first kiss. This is simply because 9 out of 10 times the girl will say no.
always ask but do it in a smooth way, like tell her you had an awesome time and the only thing that could make it any better would be a kiss! it's better than her waiting for one and you punking out leaving her hanging!