What should i do if the girl i like doesnt see me as a bf?

okay so i confessed to a girl which i have been friends for a few months. she said no and when i asked why she doesnt want to go out she brought up a series of stuff that had happened. after i cleared up the misunderstandings i finally though she was gonna tell me a yes but she said that she hasnt though of me as a bf and that she wasnt interested. later she told me that i told her suddenly and stuff along that line. then i asked if i had a chance if we spend more time toghether and she said she doesnt know.so now im stuck i cant give up cause i like her but i dont know how i can change her mind over the summer? how should i act around her? what should i do to change her mind? oh and we're both college freshmen