Replying to Basically, life just sucks

so my winter formal dance was the night before last, and the girl that i went with, i really liked alot, so i show up to take her over, and bring her flowers and tell her she looks amazing, and everything blah blah. so we get there and she just goes around and takes pictures of herself with other guys and then we finaly get to the dance floor, and dance a few times, and then we each start dancing with other people, which is normal b/c we're not going out or anything, and then i start dancing with her again, and then after that song, she just disappears. so i am looking all over for her, but she is nowhere to be found. so finally, right before the end of the dance, she shows up again, and is dancing with another guy for the slow song, the last song. so when we meet up after that, to leave, she comes up and asks where i was the whole time? and i was like i was looking for you. where were you? so she just says that she was here the whole time, so im like ok whatever. so i go to walk her back to her dorm, which is like 100 feet tops (this is at a boarding school), and i get outside and im like damn its cold out, and she just shoots me the dirtiest look ever and then i realize that she's wearing just a thin dress, and im over here in my jacket, so i offer the jacket to her and shes like well we're almost there, so dont bother. so i think to myself 'shit, i should have offered before we even got outside.' so anyways, i guess i fucked up a little, but it really wasnt that bad, was it? and now it seems like she doesnt want to have anything to do with me. so i've been thinking about how to rectify this situation for the last 36 hours straight (24 of which was my birthday - great way to spend a birthday, right?), but i cant figure out anything. i thought that maybe i should just tell the girl how i feel about her, and say like "i like you alot, and it seemed like you used to like me, but not really anymore, but i just wanted you to know that i still like you, and i want to be with you, so there's something for you to think over" like would that work? anyways, i would really appreciate any help or advice anyone can give me, and sorry it was so long.