How should I deal with this girl I really like?

Well, we are friends who met through a mutual friend (Eric) a few months ago. Most everybody I talk to say she isn't pretty but not ugly either (which aggravates me because I think shes beautiful, but that isn't the point). She is really tiny (5'1" and I'd be surprised if she weighed over 100lbs) and I'm rather large (5'11" 265 lbs). Ok, so I am a shy person as is she, but we are both very open to close friends (in this case, Eric is my best friend and is close to her as well). Being my best friend, I told Eric how I felt about her (I've never felt so strongly for a girl before) and he went to her without my knowledge and spoke with her about me. Consequently, she ended up asking me out to the movies, but a day or so later said she changed her mind and gave the "just friends" thing (she admittedly had never been on a date). Do you think that she just got nervous having never dated and backed out or felt pressured because she knew how I felt and never had any intention in the 1st place.