Can anyone help me out with a girl? need some help with a girl.?

Guys, i am 16 years old, theres a girl in my cl who i really like.sometimes i talk to her, play with her. but then sometimes when she sees me she will run away(laughing like its fun).when i ask her to sit next to me she refuses. after school she never says bye to me(when going back to home) usually i have to walk to her to say bye. she wouldnt send me txt messages, unless i am the first one to start the sending of messages,i have a feeling that she doesnt really like me but i really need her. she's like my everything now. i can spend time just thinking about her beautiful smile. i m not ugly nor fat. i get top positions in school and also athletics. But i m just a beginner with love. i dont know how to filrt with girls. can anyone please help me out? tell me what i should do? or tell me how i can know what she feels about me?PLEASE HELP ME GUYS I REALLY NEED HELP i love her alot i need HER!.