I really want to ask this girl to be my girlfriend but I don't know if I should yet?

Okay, So there's this girl I really like and right now were good friends and I'm friends with he best friend. Every time we mak eye contact she smiles and looks away and I think she likes me a little I think but the most we've ever like connected was Thursday when we had swimming together, we kept throwing the water-football to each other and when I looked right into her eyes she didn't look away and she would always throw the ball to me even tho one of her friends ask for the ball and I only threw it to her but my friends kept inferring with us so we had to always teem up to get the ball back and it was really fun we bolth laughed and had a great time also she kept trying to keep her hair dry and I thought that was kinda cute. I really want to ask her but I'm kinda shy and I don't want to mess up our friend ship because she's seemed to open up more to me than before and I do t want to creep he out and ruin what I've tried to get for awhile. Also 8th grade is almost over and we'll be going to highschool next year and I might not see her anymore I don't want to lose her she's so adorable from her looks to her personality. So please I would love some advice. :)