my binders were always loose on the top of the back of it, it puckered. Does yours do that?
I would take some scissors, and I cut a triangle out of it, you want the base of the triangle to be at the top and it needs to be the width of how much the material is puckering, then cut down and make the point of the triangle end where the loose puckering material ends. Does that make any sense? its hard to explain in words. So essentially you are cutting out the baggy excess material to fit your body more. So, cut the excess and then sew it back together. If you are not crafty or good at sewing you might want someone else to do this. Also, disclaimer, like I said I only did this to the back of my binders, not the front, and I also only did it with underworks binders.