The anatomy is a little inaccurate. The breasts should be lying more flat against the body. They cannot defy gravity and stand up like you have them. When a woman lies on her back the breast sink in and flatten more against the surface of the body.
The neck should be falling back into her collar bone more. Them seem to a little high on the chest as well. The left arm seems to be floating a little. It doesn't seem to be completely connected to her body. It is best to use a reference for nude drawings. The skin color is a nice shade though.