HELP!!! Big problem... Need expert!

I'm 19 now, I'm in love with a girl which is 4 year-old younger than me. I started to chat with her via sms 2 months ago, i did call her a few times too. I was having wonderful time to chat with her until the last wednesday, i went to talk to her in the school, she seems nervous and shy and she seems not interested in answering the question i asked. I'm a shy guy, I went to talk to her with the accompany of my friends, I was standing beside her quite long time because she was having conversation with a group of girls, I was like a nooby and don't dare to move forward to talk to her suddenly until she finished her conversation, she turned to me only i talk to her. I think she ignored me as friend on facebook after that, but i could see her online on messenger. I never tell her that i interested in her, maybe she sensed my flirt. What should i do next?

My exam is coming, I really don't know what to do. I know I need to settle this problem as soon as possible. I'm feeling down of it. I can't concentrate on my work, she is always appears on my mind, this problem really confusing my mind. Please give some advice, thank you.