Keep in mind man, She's got slightly more experience screwing with guys and shit testing them.
SHE'S push-pulling YOU and you're falling for it!
She also could be hesitant because you're not 18...She can get into trouble in a lot of states my friend.
I've been there man. Once you start developing feelings (or one-itis) you no longer think clearly. You want to see her all the time, and you lose your game.
My advice? Mix a second girl into your hang out sessions. Don't hide the fact that you're seeing someone else either. Be a man about it. Keep it nonchalant (as in, don't go flaunt it in her face "Hey, i'm hanging out with someone else tonight!") Just go do it, and if she calls you to hang out, mention that you're busy tonight.
This is going to do two things for you. 1) get your mind off of this girl 2) throw a little jealousy into the mix
If YOU don't do this first, here's what's most likely going to happen:
You aren't even officially dating this girl, and you will start acting like her boyfriend. You'll get jealous if she goes out without you. You'll wonder what guy she's with. You'll call her too many times. Etc.
Once this happens, SHE will go find another guy and distance herself from you (basically to get a way because you're creeping her out). That'll escalate your jealousy, and you will lose all value that you may have with this girl.
Keep it light and fluffy.
(also, if you're just learning Pick-up, I don't advise exclusively dating one girl right now unless she's like blatantly "the one" because you're going to get what you want from her, and then eventually, you'll want to keep perfecting your skills. Trust me, girlfriends don't exactly understand what you're doing when you're "practicing your pick up skills" they just think you're cheating...).
Good luck! Keep us posted