Very Confused. Extremly Shy? Or Simply Not Into You?

So, I honestly don't know how to react to this. There was this quiet, apparently shy type girl in my High School that I've grown a liking to. This been going along for a month now, and I have a background with stress so bear with me. This is my senior year in High-School, getting a job soon, focused on school and college for the future and a diploma. I really focused this year, because this my literal gate-way to the real world and the foundation of how I want to live it. Beforehand, that same girl would glance and walkaway with her head down when I walk past her. I brushed it off at first, because I really don't intend on a relationship this year with a girl. But as time went by, sometimes glances turns to stare and a abrupt smile and looking down; sometimes other days a emotionless face. I again just brush it off, as I have no classes with her but pass by her 5/6 passing periods by her a day. The fact she interested me because she has stuck her interest in me. The usual girl would usually get the message upon me giving my serious face, as I seem to always have it. And get the message that im not interested. But this person, literally turns to gazing at me weeks ago. Such as walking near my side to the exiting opposite side and smiling and looking at me. One big example was - my teacher was late to class and I was alone standing there waiting for the teacher as im the student aide that period; while I was chatting with a friend. She just gazed and held her smile for a good 3 minutes at me, as I know cause im the only freaking guy in the hallway and my friend was facing from behind to her. Being the over-thinking person as I am; I thought maybe she that's just her attitude, (dresses in Kuro Loli clothing, google it) Is there something on face/expression? Or maybe she likes the way I dress? Stupid trivial things like that. It wasn't untill yesterday she literally paused and stopped to turn around at me and smiled. I won't lie, I was intimidated and thought wtf as I gave a respectful smirk as I entered class nearby. One would think, that be the signal to approach somebody, so I did the next day. So today I decided to, ''break the ice.'' And write her a note and directly give her to her when she waits to get in her class. As I was approaching her, from a distance she smiled and I smiled back for once openly and approached her note in hand. Thing is, she raned away when I was face to face with her; smile turned shortly to the non expressive face. I was left hanging there just paused with the expression, ''. . .'' Im going to be crude, because I have problems trusting people and generally opening up to people. Seriously? This crap happens to me the first time I decide to open up to somebody? Seriously wtf? My friends jokingly says, ''maybe she got disapointed in your face as you got closer.'' (You judge my profile picture) ''Maybe she's beyond extremely shy.'' I do not know, hence why im posting. I apologise for any butchering of punctuations and spellings, im writing this on my smart phone. Thank you for your time, hope you can help.