What did I do wrong as she isn't returning my calls after we kissed?

Well, at this point, it would be advisable to not to overthink about it. It could very well be likely that you did n thing wrong and that she was carried away at the particular moment. Perhaps she is not ready for it after all, and wants to take some time to think about it.

Or it could also be very well likely that she was bored at that particular instance, and hence wanted to feel some temporary affection. You could never find out what happened unless she tells you of course. So instead of stressing out on it, move on and look forward to the rest of the bright world.