Pretty common experience with the belt. I felt similarly when first squatting with a belt (think I tried 275). When I first started using one, I had a problem of collapsing in and out of the hole, and using a belt had helped me feel how to keep my trunk tight into the bottom of the squat.
The bruising may come and go for a while, depending on the extent of your gut (worse if you're skinnier). I remember it intermittently for the first year, but never for it hurting, more as a "hunh".