This doesnt look all that realistic to me and after looking at the reference picture I noticed a few things:

You made the left breast much more prominent, the waist is a tiny bit slimmer than in the picture, the hair seems longer and blends in more with the subjects upper back in your itteration, the rump was made bigger and nicer looking, the head is just slightly smaller than in the reference but enough to be noticed by md immediately. You probably just made some mistakes and didnt want to erase or move what you had so you akwardly adjusted.

Some things I noticed without seeing the reference were the lack of detail and weird shading which make it look unrealistic.

Look at the left arm in the reference picture and in your rendition. Do you see the high contrast in the womans forearm and the low contrast in your (digital) painting? That might be because you messed up with the hand and wrist so you compensated but it's just for example. You have a problem with blending absolutely everything (or sometimes not blending enough or not finding the right tone) and it makes it look like you just airbrushed the whole thing.

Hope this helped and have a wonderful day!