I liked a girl but then didn't want to go out with her anymore because she's not physically attractive
What made you change your mind after asking her?
I saw her and that was that. She wasn't my type.
It is normal to have preferences when you are dating. As long as you aren't disrespectful or rude, you did nothing wrong.
I don't want to date her.
It's fine to not be interested in  dating someone, we all have our own preferences. You should just be sure that you are not harsh about letting her know.