I agree with Al.
You have to move your marbles off of the Lego Kit before taking an image.
It does no good for your images and throws them off a bit.
Try a Grey cloth like @Chad G.suggests.
Chad suggested this stuff to me a few years back and I will never look back.
https://www.amazon.com/gp/product/B07MNR63QC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Cheap and lots of it--it takes a photo very well. Search around, you may find different colors.
Marble--On!!