Her boobs are uneven, and the left nipple is positioned way too high. If you imagine her standing or sitting straight, then her nipple is almost at the top of her boob. The other one is positioned too high as well, although, not as bad as the other one. But, they are uneven, nonetheless.
You should also be able to see a very little bit of her belly button, her arm is not covering it up entirely, but you have not drawn it in. There is nothing on her stomach, it has no texture or shaping, it is just empty, and that makes her look funny.
I love her legs, you did a great job with them and her kneecap is very realistic.
She also has a very beautiful face, I love the expression in her eyes and the way her lips are shaped. She looks like a woman who would kick ass if needed, but in this picture she is giving the "I don't give a fuck" face, and this is amazing. Her legs being crossed paired with this facial expression keeps her classy while still saying "fuck you" ha ha.
Her hair on the left side of her should have a bit more volume, because the other side has that much height it shows that she has a medium or average hair volume, and it shouldn't be so flat on the other side.
What she is sitting on, the blanket seems rushed, especially the bottom of it where it is balled up from extra length. I love the background of it though, how there is all different shading colors patched together. This is not realistic at all and it is obvious that you meant it to be that way.
Oh, her feet need more detail, give her toes at least. right now she looks like she has socks on, but there are no socks. If you penciled in a line on her leg to make her have socks, that would be quite awesome. The fact the she is naked with her expression and her legs crossed, wearing nothing but socks is a sexy idea. If she was holding a cigarette carelessly in her hand on top of that, then this picture would be perfect.
You should fix her nipples and even out her boobs, that's the only part of this picture besides her toes that really bother me, a lot. It looks creepy, ha ha.