I approached a girl a day ago and i told her that she was beautiful and i wanted to talk to her, at first it seems to me like she was confused or surprised? I asked her if she does get a lot of compliment like this, i kinda remembered she said no. Then she said she wasnt beautiful and that she was the most unattractive girl in her class. What could she mean by this?

And if this does happen again with a different girl, what should i do? I think i would want to relate to her about the feeling of not thinking yourself as attractive but would like to see how others would go on about it?