I suggest you give your camera away to somebody that could actually...no, no. Just kidding.
So, what are you trying to achieve here? Is it just a light study/learning experience?
Try some compositions with the "horizon line" not in the middle.
I like what you're trying. I think you should get your marbles away from the backdrop.
I know, you'll lose your marbles if you do. Solution? You could try table salt to rest the marbles on in position, and carefully blow away the excess. Better would be some sticky wax, like beezwax. Use very small amounts, and work clean. I say this because I am not totally digging the harsh line where the floor meets the back.
There is also a product called jewel gel, or something. I can't find it, but I know it exists, and have used it. It probably has some funky spelling of the name. Anyway, it is crystal clear, clean, and very very sticky. Perfect for what you are doing.