I love a girl, and the feeling is killing me?

I love a girl I've known for 3 years, I'm 13 and I want to tell her really bad. I'm gonna tell you about something that happened a few months ago. I was chatting with my friend, and he told me to ask her out in fb and I asked her out and he said that if she said no then I'll just blame it on my cousin. Well I didn't understand well, I blamed it on my cousin seconds later after I msgd her, I didn't let her answer. She didnt reply back. Then my friend asked her if she received the msg, she said what msg. She knew what msg he was talking about and then he said nvm, she found out it was a lie when I blamed it on my cousin. Since I'm a fu**ing idiot and I'm shy, one day when she called my name she smiled and I didn't smile back, I just said hi and walked away because it was gym and I was playing a sport, she was sitting in a table. I feel really bad for it. She has done many things that look like she's showing that she loves me back, because she has made statuses on facebook that are really strange. Sometimes she stops talking to me and then I want to say hi to her on fb, but she doesnt reply back now. One of the statuses on fb was made the day I didnt smile back, it says follow me on twitter, but one of her twits say "Keep on smiling, while ppl dont smile back" Another status "I thought that our love was strong and nothing could go wrong