I'm in the same situation DaQ.
It's like you and me are the same guy.
I'm going to ask the chick I want to go with tomorrow (If she's there, cuz a lot of seniors are ditching due to STAR testing). If she isn't, then I'll be ready whenever she decides to come back to school (which would be later this week, possibly next week)
Remember (IMPORTANT)... You gotta be certain that she doesn't have a date when you ask, otherwise you'll look like a fool.
Hope everything goes as planned!
I wish you luck.