Is the stand from a box? Or did you build it from scratch?
You could use a piece of plywood over the top of the stand. Or if you built it fix the issue. If it's a kit from a box make sure everything is in the correct position and put together in the correct order, that can throw it off on those kit stands. Trust me it sounds dumb but if they are labeled in a certain order do it that way. Even thought it may go together it may not sit flush. I've built quite a few of these and quite a bit of stuff from IKEA also.
It could also be the kit stand is just not made properly, wouldn't be the first time I ran into that.