I just got rejected but I don't feel that bad about it why?

This girl was really the first one that I really liked. We went to the zoo together last Saturday and yesterday night I asked if she wanted to hang out again and she said she was sorry but she just wanted to be friends. I kinda thought she would say something like that since she is a lot more popular than me and Im honestly surprised she even went with me the one time. I really just didn't care that much and I don't know why?