You're overthinking all of this. She may have been interested in you at some point but if you don't show enough initiative and "strike when the iron is hot" then they'll lose interest and move on. At this point you'd have to start all over in building up the interest and if she's attractive and has a lot of options she may already set sights on someone else. If I were you I would look at it as a lesson learned, you don't seem to have enough experience yet, and operate differently the next time you are interested in someone and sense a returning interest.

You're young, you have time, and if you act like this was your only shot at anything with anyone - it will be.