As you're nervous about it and it sounds like she may be too, best you approach her where not too many other people are around. It only takes one other schoolkid to overhear you and you'll both be teased something rotten. Maybe also prepare at least some of what you'd like to say to her. But just suggest something light, like meeting for a coffee or going for a walk, initially. Movies are hopeless for first dates because its hard to chat in a cinema, and you cant see from her eyes how she's reacting to you. It may seem a good idea to say something like "I really like you" before asking her out, but it seems you've not spoken to her before so she'll assume you just fancy her physically. I'd just say something like "Hi, I know this may seem a bit forward, but I was wondering if you might be interested in having a drink with me sometime." Brace yourself for a refusal, but hope it's a yes. Good luck.