I don't think a person's appearance is what makes a person "ugly". I think it has a lot to do with attitude and how you treat others. I'm attracted to those who are positive and happy. Size doesn't determine that.
You very much a pretty girl unlike you (from what I can see) some just care how they look and wear clothes that make them look unattractive. And plus many are not because of their and whatever so many come as a ugly person. But from your picture you have a beautiful smile and as long as you keep smiling and carry yourself with pride you will always be beautiful. And not just big that are that too.
I don't think size affects beauty, people are beautiful no matter what size they are. However, I can't help but think of the extra stress their body is under to sustain the extra size. I lost a lot of weight recently and I think it gave me a new perspective on weight.