Nice composition and structure.

Pay attention to foreshortening of the shadows.
As objects are along our line of sight, they get foreshortened (distorted in that direction).

So, while the structure is a ball or a cylinder, the shadow is not a circle, but an ellipse (and it usually has soft edges):

In addition, I would add some dark areas, so the structure won't look flat.

I think you have good accuracy. A bit more work on it and it will be great.
Good job, and good luck.