How do I ask her out? Please answer!?

[Roelito]

Background:

So I was on 'Twitter' a few days ago, and a girl, that I'm currently interested in, tweeted that she wanted someone to direct message her. I took the "bait," and direct messaged her. She seemed interested. We kept messaging each other, and I made her laugh a few times. I asked her for her number that same day, and she gave it to me. Today, at school, I saw her a few times. She said, "hi" to me, and I said, "hi" back. I recently just text messaged her, and we had a short conversation, but she stopped replying (which is probably a sign that she isn't interested in me).

My question:

I think she's pretty cute, and I want to make her my girlfriend. We're both in high school. She's in 10th grade, and I'm in 11th grade (so we don't have any classes together). I want to ask her to hangout, but I think it's too sudden. I don't want to screw things up by acting too early (if you know what I mean). I messed up with another girl, and I don't want to mess up again with this girl. How do I achieve this goal? Please answer! Thanks!