How to ask this girl out? Please help!?

Okay, so I have been "together" with this girl for about a month but technically we aren't dating. We hang out everyday, we kiss, all of our friends think we date, we've even had and she actually spent the night last night alone. We both go to college in 3 weeks and her college is only 30 minutes away from mine but I don't know if she wants to be single for college but at the same time she acts like my girlfriend all the time. The question isn't if she likes me, it's more of how to figure out if she just wants to be single and how/if I should ask her out. I'm just afraid of being rejected but I figured I might as well ask and see what other people's opinions are.