What should I do??

Im 15 years old, and a freshmen. (Sopre in September) Theres this girl that I met this year in my math cl and I really like her alot. Shes a Year older then me since im in a higher level math cl. Everyday when she walked in the cl she made me start smiling and we say hey to eachother. Sometimes we make fun of eachother for fun and she scoots her desk next to me for help sometimes, we always laugh together and stuff. We also both play tennis and run cross country, I feel like I have a real connection with her and I like her SO MUCH, and now its summer and I can't stop thinking about her, I was thinking about asking her out next year when I return, but im so scared lol. Please help me :( and how do i know if she likes me??