Last week of school with this girl?

I only have 2 more days of school. They are exam days. I'm not ready for school to end yet. There is this one girl I like but I haven't told her yet. Monday I have an exam in the same period. The exam will only take a few minutes so we'll have 2 hours in the gym. We are only casual friends but I want to sit with her and get her number, maybe ask her out if it seems right. This may be my last class with her and I have 2 hours. Good idea? And if you're a girl, how do you react to that durin your last week of school?