So should I go for it?

ok, I'm 15, and there's this girl I've known since we were like 3. I have always liked her, and she knows it. I just spent saturday working with her at a fair in Kansas. She stayed by me the whole day. We ate lunch together, just us. We went to a zoo like five minutes away and it was her idea. (we were there for an hour) Just me and her. Dr. Pepper is her favorite drink, so it was her idea for us to go get some. Then we ate dinner together. Then she wanted to ride on the night hay ride, just me and her. So we did and it was like a 45 minute hay ride, it was freezing cold. The whole ride we laughed and had a great time, with her attached onto my arm and shoulder. Then we had to figure rides to get home. There was a car with just 2 seats, and another with 5. She asked to go with me in the 2 seat car. She spent half car ride (now 12:30 at night) asleep on my shoulder, and then the other half resting her head under mine and snuggled up to me. Should I ask her for a deeper relationship, like boyfriend/girlfriend?