I like this girl from a long time and i feel really sad.what do you think i should do?

back 4 months ago i had the courage to walk up to this girl in the lunch line at school(im a junior) and so she talk to me and it went well. i thought she liked me becuz she was nice and paid attention at what i said.anyways i ask her to this carnival and becuz she is in advance classes she said it depend on her hw but she never mention it again.i use to carry her books. by the way i dont have any classes with her.i only see her rarely now. anyways i use to see her at the library and we had an awesome time from my perspective but i dont see her at the library anymore so i think she is tryin to ignore me. anyways i wish i could tell her how much she means to me. i like her so much for who she really is and everything about her. what makes me the most sad and depress is that i think she doesnt feel the same about me.i wanted to write her a poem but i think she might see it as a stupid thing. i like her so much. help me please? and no jokes please