Asking a girl out?

there is a sadie's dance at my high school and there is this girl that i really like. We sat next to eachother in computers cl and she asked for my number. We talk during the cl, and in gym when we have time. She also im and texts me quite a lot. I also gave her some chocolate after she broke her ankle during a soccer game. I know sadie's is supposed to be about a girl asking a guy out, but all of my friends have dates, and i think that i should ask this girl out. I know you have to be confident, have a backup plan, and all that stuff, but should i wait for her (not sure she will) or should i make the first move? Any advice on a creative way to do it, or even if i should ask her at all?