Asstates, the answer is basically buried in the question, though I'll go a bit deeper:
- Ugly, by definition, is not tied to a particular body shape or size
- Cute, by definition, is also not tied to a particular body shape or size
- Predictive level of health status and issues, however, do come closer to mapping to a specific range of body sizes – too skinny is seen as unhealthy, as is too fat
I think that, casting direct issues of anorexia, obesity, predisposition to diabetes and the like aside, what it comes down to is this: attractiveness is based primarily on what you DO with what you've GOT.
For example, I go to Japan fairly regularly… And I'm always reminded not only of how much generally larger American women are in the strictest sense, but also in how much cuter the average fat Japanese girl is, compared to her American counterpart. This isn't a case of "Yellow Fever", but rather an observation that women in Japan, regardless of their body type, seem to have a much broader and better understanding of how to make their particular legs/hair/physique work in combination with the fashion, makeup, and beauty regimen they can afford. I hate to be this blunt and overgeneralize at the same time, but it seems to me that a lot of the time, if an American woman feels she can't be one of the most beautiful women in the room, that she tends to scoff at the very idea of striving to be beautiful – turning her defensiveness and anxiety about her looks into a more "respectable" pseudofeminist political statement.
This is definitely not something women do on their own – a lot of the western fashion/beauty industry caters to a very small subset of females… If the latest dresses aren't flattering on you, you'll quickly find that the much better stuff from last year's collections have all but disappeared. This doesn't seem as prevalent a force in non-Western countries. In Japan especially, every single fashion fad that every was, lives on today and probably will continue to exist far into the future.
In short, whether you are skinny or fat, or anywhere in between, being cute (or ugly) is mostly up to you. If you want my advice, I'd suggest trying to find the cute that works for you, and the people who find that attractive… And spend a lot less time worrying about small-minded detractors in the world at large.