I like underage girls.
Do you mean you sexually like underage girls?
Yes. I'm attracted to young people.
This attraction to underage girls isn't good. You should seek counseling for it so you can try to fix the issue. It's most important though that you never act on these feelings or you will cause permanent trauma to someone.
You make it sound bad, but I don't think it's wrong to like them.
Acting out on these feelings you have by actually having sex with a child will traumatize the child for their entire life. Sex is not something that children can consent to or are mentally prepared for. You need to seek help before you do something that causes this kind of harm to someone.