I agree with the general consens (especially Averett's last remark):
Call the girl up, explain the situation to her (you have a girlfriend), and I'd also tell it to your girlfriend (so that if nothing else it doesn't later turn into a "why didn't you tell me about that girl?" argument).
But yea, I've had situations where girls have given me compliments, one in particular that was amusing when my girlfriend was nearby, and she's gotten laughs out of them.
