If you are trying to do it as a nondestructive layer I think you've done a great job. The only small nit pick is that you might have a floating creaseline at the bottom of the folds and maybe play with some highlights as well as shadows. That would be really really finicky though and might not be worth the effort.
My comment above was really based on this tutorial for Photoshop.
http://www.planetphotoshop.com/folds-and-creases.html
Its very thorough and very good but it does deform the image.
Sigurd