Talking to a girl and I need help?

I became interested in this girl this weekend when we spent some time together at a fair. Her name is Sarah. I got her number at the fair and have been texting her awhile. She defiantly is more of a face to face kind of girl, she NEVER leaves something to talk about, at first I thought it was just because she wasn't interested in me, but I spoke to a couple of her friends who I've known for awhile and they said that's just the way she is. Anyway, in one of the texts i sent her today I said "You looked really pretty at the fair the other day" it took some guts because I'm not exactly a "ladies man" and I was hoping for a happy response. The text comes in and all it said was "Oh thanks" I have no clue what to say to her now, and I know she doesn't have a boyfriend. I'm 14 turning 15 soon by the way, and yes, I'm serious about this girl. And I just want to know maybe how to get her to open up more to me, or get her to realise that I like her.