How do i get girl in this situation?

Hey guys, i need some help with this girl. Alrite heres everything. Were juniors in HS. Friday is our last day before finals. This girl i've liked is really quiet and only talks to a few other girls. She doesnt talk to any other guy at all, NONE. shes really cute and i really like her. We've never had a ongoing full conversation before. So last friday, knowing the end of school is coming and being uncertain about us having classes next year, i decided to grow a pair. After the bell rang i walked up to her and said "hey {name}, i know we never really talked, but i was wondering if you were doing anything this weekend." she said "Oh, yea.....sorry" and walked away. I felt like trash the entire weekend until i learned she actually did go somewhere with her family. Tomorrow is last day of school before finals. Today i wanted to go up to her and talk about the weateher or sumthing but it seemed as if she avoided eye contact with me. I walked into last period a little late, and normally i would see her first in class room(shes like 4-5th row first seat) but the very second she saw me she looked away and when the teacher started to hand out papers(i sit 2desks behind her but kid in front of me was absent) she didnt even turn around to hand it to me or collect later on, just put her arm behind. Today in first period, out of the corner of my eye i noticed her looking over a couple times. I finally looked her way and the second are eyes met she looked foward. I know im going to have to msg her on facebook now to try to talk to her or talk to some people about going to beach in a group, and try to get one of her friends to get her to go. Can someone please play the roll of hitch for me. Explain whats going on and what i HAVE to do. Im not a bad looking guy at all so its not like im ugly. I got a 6pack and muscles etc. I fell hard for this girl REALLY REALLY hard. My friends told me shes to skinny, flat, quiet, not that good looking but i think shes simply flawless. HELPPP!!