How do I keep my cool? I want her to be in my clutch baby!?

I found this girl that I knew in 10th grade working at a store. And I could do nothing but smile at her. She smiled back at me. I was in the customer service line and she was dealing with a customer after that was done I said how are you and recollected. She was fine and slim, b cup rack, lol, with a round with these tight jeans on. And she had one pretty face. I was talking to her about working in the same store she was working at and where I should get the application, she directed me. And after I went back on the line. She gave me this priceless look like 'I can't believe this guy.' I went on line and asked, "Can I get your number?" She said I was mean to her b4. I was like times have changed. I she was like I will give you my number tho. How do I talk to this chick, she's a little above my status and I'm in 12th grade while she's in college?