If she doesn't call back, let it be, try again in a couple of days. It's no big deal if she gets back to you or not right?
If you want to get a girl back to your place (on any given night), you have to work on getting her IL up. If her IL (Interest Level) and attraction is high, you could probably bang her at a stop light on the 'way' to your house.
If there is a pattern when it comes to girls getting flaky on you after showing interest, your approach could be off. Are you turning into wussy, needy boy after she gets your attention? Something to think about...