the way you positioned the marbles make them look very flat, like a 2D image, probably due to the different sizes of the marbles. and when you lay them like this, looks like all the same size...
your post processing have some problems. the picture is overly sharpened, look even more 2D.
I think a change of angle, change of positioning will help alot, esp without the 4:3 look... a 16:9 would be better.