Issues with getting my hands in a girls pants...(respectfully of course)

Sexxit, recently I've been having some girls over to spend the night with me. Most of the time, these girls will come from out of town to visit me in college and stay in my dorm. When it's time for bed, we both get into bed and waste no time getting comfortable and making out. My issue from this point is making her comfortable enough to finger her. I always start by slowly caressing her legs, slowly making my way to her. Once near, no matter the girl, she'll pull me away and continue to make out. This will either transition to a hand job for me (nice but not the best), or more making out followed by me falling asleep.

Advice from you Sex gods?