I'm a senior, she's two years younger. There's been flirting, sexual tension, and general hanging out prior to this, for a good 6 months or so. She isn't available for long afterward, which sucks. Any suggestions? Let's be practical please haha.

EDIT: Sex is highly improbable, but kissing is fair game. Haven't kissed her yet. Advice on that would be cool. Btw prom is tomorrow, and I'm taking her out to lunch beforehand.