Not bad. You have pretty much all the elements from your reference in here. But there are some things you can work on.
For this study I think you should just work on blending, hard edges and soft edges
An example of soft and hard edges can be found in the clothing.
I recommend studying the planes of the faces as well. This will help you learn where to put shadows and what areas would be different values or tones in different areas of the face.
Another thing I would add is to spend some more time on the study. Set a goal for what it is you want to learn when studying as well.
I did a paint over showcasing some other things as well.
Keep up the good work. Look forward to your next piece and or study.
