Is it too late to ask her out?

I'm 17 and looking for a little advice. I've liked this girl for a little more than 3 months now, and we've been talking ever since. We haven't really hung out much, with the exception of prom, which we both had a great time at. However, prom was a little over a month ago and I'm afraid she's losing interest, as we really haven't been talking a lot recently. I know that she knows that I like her (I did a pitiful job of hiding it) and wasn't sure if she felt the same way about me, which is primarily why I decided to wait. I know as far that she gave me signs a few weeks ago implying that I make my move, however I totally missed them, am I'm afraid that I've waited too long. Is it too late? Any advice would be appreciated. Thanks.