Oh I've done this before... loads of times!
If the girl likes you, she'll be as annoyed as you are for not getting a kiss.
See if she wants to hang out with you again. If she does then she probably really likes you - and if she really likes you, you should probably just kiss the poor girl.
If you can't seem to find the right time to kiss the girl, you need an excuse; start playing a little rough with her by pulling, pushing and gently hitting her. If she's cool she'll start playing back which will give you the opportunity to pin her to the floor/wall/couch and go in for a kiss. And if she gives you any shit about acting like a five year old never apologise; just give her a big cheesy grin, and say something daft like, "Well, I've got to do something to amuse myself around here!".