A twenty-year-old co-ed does not need to wait two weeks to see a guy and judge his reaction in order to determine whether her booty call is still viable.
If all you ~really~ want is some sex - you could easily set that up over the next two weeks and be blowing this guy off the next time you see him. I'm just sayin'. The men at your age range are more than willing to keep it simple for some booty. That might be the approach I take. Replace him with someone outside your circle.
As for you not being ready and needing to figure things out...look, that's what 20-year-old guys are for. They are cannon fodder for women trying to figure out what they really want! As long as you pay the price for your indecisions in booty, the guys will line up to sign up. What better way to figure things out than to date a decent cross-section of the available populace.
Figure it out now, there's no expectations at this age. A guy in his late 20's has far less tolerance for soul-searching than the walking erections of the early 20's.