Trying to figure out what girl means by "I'll let you know"?

Well there is this girl that I really am attracted to, and am trying to pursue. I asked her out once, but she was going out of town so it wouldn't work. So when she came back and I saw her, I tried again. This time she says she is busy and that she will let me know. In my head I was thinking that, that was a No and I should move on. Then again I have been told that I give up too easily. Currently, I am thinking should I wait a few weeks and bring it up again? Not to mention if my current assessment seems correct.

I should also mention I had gotten her number prior to this and she answers me very sporadically, which to me says another thing. I just don't text her all the time, and only once in a while (even then she might not necessarily answer). Thanks for the advice in advance.

Trying to figure out what girl means by "I'll let you know"?
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