Reddit reviews 2041-12 Stories About the Future

No, as the link clearly says, the name of the story is "Lose Now, Pay Later". Which is the right story.

And this is the anthology I read it in as a kid.

"Ear" by Jane Yolen, in the anthology 2041: 12 Stories About the Future.

In the one I read, they got the marks on their wrists. Also, it was that, first, free sweets shops started opening up all over town; when the people started getting unhappy about being fat, weight loss-machine places opened. The only payment you had to give was getting a mark on your wrist. Towards the end of the story, the marks began to look like bracelets. It ended on a spooky sort of not-quite-ending.

If this is your story (although it sounds kinda different from what you posted), I'll try to look up the title.

EDIT: I got interested (or nostalgic) enough to look it up anyway. The story I'm talking about is called "Lose Now, Pay Later." It's written by Carol Farley, and can be found in several anthologies (notably, this one).

Could the story be "You Want It Now?" by Kara Dalkey, from 2041 by Jane Yolen? I don't have the book with me, so I'm not positive.