How do I get this girl?

I am 15 years old. I just finished my sophomore year in high school, and throughout the year I have been getting more and more into a girl named Lena. Lena is a cheerleader, extremely outgoing, very popular, and well I think you can picture her already. Extremely hot. I have hung out with her a few times and we have actually gotten quite close. She is actually very insightful and understanding and we help each other with problems. She has told me a few times that she could "see us dating in the future," or that "she's probably going to marry me" or that "she would have sex with me if we weren't so close." She has said all of these things on her own without any of my initiative. I usually have no problem flirting with girls or getting a girlfriend, but she seems different. I am outgoing, yet I rarely flirt with her, and if we do ever flirt she starts it. I guess I am afraid that she doesn't see me as more than a friend. I am pretty sure I could make her my girl, I am just not sure how to go about doing it. I don't know if she is playing hard to get, or if she doesn't like me at all, but so far I haven't been successful. Just a little advice please!