It’s likely that if she had a great time, she’s going to most probably to (or possibly even suggest) potential future plans together. Maybe you guys talked about how you both haven’t seen that new movie yet or dined at that restaurant around the corner. That’s a pretty obvious in for a date in the future, and if any of this type of conversation happened, it’s clear: your date went pretty well. And if you went so far as to discuss times that you’re both free next week, we don’t even have to tell you that your date went well.
You can safely exit this article because the question is already answered for you. Try not to over-analyze the words that she says at the very end of the date, because generally, they’ll sound pretty similar, whether she had a good time or not. If you say your goodbyes and she had a good time, she’ll probably say something like Hey, that was a fun, I had a good time.” Meanwhile, if she just wants to get rid of you, she’ll probably say something like Hey, that was fun, I had a good time.”