Also it would help to get photo reference of cloth that's hung in a similar way to the arrangement you're trying to create there. How exactly is your cloth attached to your cart? The folds and creases would be directly related to this. For cloth, photo reference is key!
The cloth folds should be a lot tighter / crisper towards the corners, where they are getting pinched, and a lot thicker and softer towards the middle, where the weight of the cloth would be. Try varying your brush size/hardness, and making sure you use less opacity when painting the folds toward the middle of the cloth.
Heres a useful tutorial I found on painting cloth, it focuses on getting the folds going in the right direction, may be of use :) http://www.store.forbiddenwhispers.co.uk/freestuff/tutorials/ClothTutorial2.pdf