Looks good. Yeah, I did the same thing, I made the tubs fit with a little play, not realizing that the bins will flex a bit and prone to falling out. I ended up slapping some more wood on the rails that support the rack so that the sides of the bins are touching it.

For more support I would add diagonal bracing to the sides. On my racks I also used a piece of masonite about 12" wide all the way down the backside as my stop. That also helped make a huge difference in sturdiness.