From what you say, I assume you mean that the pedestal itself does not have a flat and level bottom. If your floor is flat and level, your problem is that the manufacturer of the sink pedestal has screwed up. Take the unit back to wherever you got it from, and get a good unit.
I suppose you could try to shim up the faulty unit, but why should you have to do that?
A reputable manufacturer will stand by their products. I’ve seen a few low end pedestal lavs that are manufactured in Mexico and sold thru places like Home Depot that have the kind of quality control problem you describe. Thank you, NAFTA…