So the fish scale and rock textures are a bit small, I would recommend getting pictures more the size of the wood texture. But they're workable.

The first thing that I noticed is that you do seem to be working a lot from memory. The left square is supposed to be an exact recreation of the shadows in a part of the reference. But there are signs that you did not recreate the reference in all 3 rows: the small triangular shapes I see in your wood analysis are not in the reference, the rocks are all different sizes instead of being roughly the same size, and the scales are facing the wrong direction. The line on each of the fish scales I also do not see on the reference.

You need to draw what you see, not what you think you saw, or what you think wood, rocks or fish scales look like. That's the difference between drawing from observation and memory. This involves looking at the reference every time you want to capture something, then putting it down, then looking at it again, resulting in about 90% of the time looking at the reference and 10% of the time actually drawing.

As for cast shadows, you should only be capturing the cast shadows you see in the panel on the left. Right now, you are still drawing explicit form outlines. The way to think about cast shadows is to see what forms are present, then think about how they would cast shadows on their surroundings. In references like the rocks, this is easier, you can draw the cast shadows (dark areas) that you see directly, in others you will have to think about where those cast shadows will be. But at this point, getting this perfect is not a big deal, there's going to be a lot of form and texture practice required. Just make a goal to capture cast shadows.

In the third column, you try to manipulate the density of cast shadows to create a gradient. The best way to approach this is to start in the middle with drawing cast shadows just like you captured on the left. Then, moving to the left, make each of the cast shadows you draw bigger, join them together, ultimately making them solid black like the black left bar. Towards the right, shrink the cast shadows until there are no cast shadows left. Think about a hierarchy of cast shadows here, the deepest shadows will be where multiple forms intersect, while the lightest area will be on the surface of the forms. The deepest shadows will be the last ones to be removed when shrinking shadows, the lightest areas will be the last to be filled with black when growing shadows.

Hope this helps.