You have a choice to make. You seem to like the sisters, and evidently they like you, otherwise you wouldn't have been offered a bid. So you have to decide what's more important to you: your sisters - both in your chapter and elsewhere - and the lifelong bonds you'll form with them, or the sorority's reputation as "the fat, loser one".
Reputations change. It takes time and effort, but reputations do change.
Frankly, if you are at a school with a competitive rush, and you depledge and re-rush next year, you are unlikely to get any bid at all.
Carnation, I've never had Cherry Vanilla Dr. Pepper, but it sounds delish - got some for me? And I'm baking chocolate chip cookies, if anyone wants