I'm going to end it with a girl who didn't find me attractive
Why were you trying so hard in the first place if she didn't find you attractive?
I thought if I improved myself, I could win her over.
It's not wise to date someone who thinks that you are ugly, because she might ditch you, or would be constantly criticizing.  As long as you feel good about yourself, you shouldn't care if one other person doesn't share your opinion.
Exactly.
I'm glad you see it that way. It's never a good idea to base a relationship on what we want the other person to be, rather than acceptance of who they are.