Alex, remember that a binder can relax a bit after only little use. Unless your binder is uncomfortably tight, you might consider the next smaller size. It might be a bit too tight for a week or so, then it could relax and be just right. I suppose the amount of loosening depends on the material. You might ask around and see if people noticed whether the same model did loosen up.
There is an older thread around here that you might look up. Guys gave their measurements and said which binder they were using and what size and all of that. It might give you some ideas about how a smaller size would fit your particular anatomy.
Honestly, I'm thinking that you will probably want a couple of binders anyway, unless you're really short of cash. So you could order the smaller size and then return whichever one doesn't fit as well. I guess you've had the medium for a month now, so maybe you can't exchange it. But if you order a a small and it doesn't work, you could always exchange it for another medium, and then you would have two. And you would know that the small doesn't work. You'd lose the shipping cost, but knowledge is power.
ETA: You might post pictures from other angles. I don't think you look bad at all, but I can't see you from other perspectives.