I have this one that's from the same company but after 7 months of consistent use it's only wrinkled where I tie it off. It's a really, really thick cotton fabric. It's not perfect anymore but it seems to be doing pretty good.

My SO has this one, also the same company but also doing pretty well. He doesn't use his nearly as frequently as I do.

Maybe the one you bought just has a thinner fabric or something? Or maybe I got lucky.