How do I talk to this girl?

[Kevin]

I'm 18 and she is 16. She sits in front if me in one of my classes. She has recently has been talking to me. It's just small talk like 3 times so far but I never talked to her before but she said something things to me this past week. Today this guy was saying hi to me and she kept turning around and looking at me. When we were talking for like a minute she was looking right at my eyes the whole time.(apparently I have really pretty eyes) I don't know what to say to her or eventually text her cause she doesn't have a Facebook or twitter and idk anyone that has her number. I'm scared to ask her for it plus I'm a shy guy! I asked my friend about her and she said that she is obsessed with this one guy. What do I do? HELP

[N]

If you want her number but don't want to blatantly ask then just say something like could I have your number so you could help me with homework or to ask what the homework was. Something along those lines.