I started talking to a girl in order to start a relationship with her and I wish I had not.
Is there a reason you feel this way about the girl?
Her boobs are smaller than what I imagined
While it is okay to experience regret when it comes to meeting new people, it isn't appropriate to regret meeting someone just because of their physical appearance. It shouldn't have mattered if that person you met had smaller breasts than you imagined, they are still a person and are just a valid as anyone else. You should try to be more open minded and learn to appreciate people in ways more than just how they look.
It's not my fault that such things limit me.
Shaming and not liking someone due to how they look is shortsighted and unkind. With this mindset there is a big chance that you could miss out on a great and fulfilling relationship.