She rejected my Facebook friend request.... but why?

So I had this girl in my class who I really liked and I could tell she really liked me as well. I always saw her looking over at me in class. I talked to her from time to time but I was too afraid to ask her out in person so I never let her know that I liked her. Well after the semester ended I sent her a friend request on Facebook and she denied it.

Is it because she thinks I'm too much of a wimp or another reason? Thoughts?
She rejected my Facebook friend request.... but why?
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