Problem is you didn't escalate at the club.
That's an insult to the lady. So she gets your number at school. Do know that women don't do that. She gets you interested in her - because as she previously thought you're not interested in her - with the sole purpose of getting back at you. Which she can readily do by denying you a date every time you call. Nothing you can do now.
First thing is escalate, always. No such thing as too far. Small steps, and take 1 step further. She'll always let you know if she's not comfortable. They get flattered when you escalate, they get extatic when you take it a bit too far.
Second thing, when a girl says she can't go out with you, tell her she's screwing "this all up". Demand that she does go with you, or else, she's going to loose it all. Follow up on this principle, always. She says, you dont' understand, I can't today. Ok, good byyyyyyyyyeeeeeeeeeee. That don't mean you lost her, she'll come back (not you come back). Then you could give her a second chance.
How to handle this school girl. Don't. Remember what she did to you. Just because you aren't experienced. Shallow rat. Walk by, you see EC, EC back, and smile. Don't talk to her. If you have no choice, say you gotta run. Instead, talk to other women and men. Sociolize. Forget this rat. She might come back in the future, but that's only to fail you once more.
Protect your ego. If she literally approaches you and would like to find out if you two can go out. Tell her I assumed you were a cool chick with values I'm looking for, but you've lied, there is no future between us. If she says anything at all, tell her, I only talk to women I'm interested in fvcking. Then don't talk to her from that point on. It's like reminding her that you wouldn't want to touch her even with a stick every time she speaks to you and you say nothing.
See how sh1tty women are? There is no such thing as escalating far enough. Even the furthest point does not equal of such crappy behavior women do all the time.