Charlie
A tabletop only really needs one, flat side and that's the side that fits to the apron. Any twist can pull the undercarriage itself into twist when the top is mounted. If you've left enough trim room on the legs you can make the table sit flat, but it could mess up the fit for any drawers included in the design.

Unless the surface exposed to nothing but air is egregiously out, and of course it shouldn't be, nobody will ever notice. The only requirement for this surface is that is be attractive cosmetically --smooth, etc. it does not usually have to be a geometrically perfectly flat surface from end to end and across its width.