Looks more like it's been put down on something rough, or some rough heavy things have been placed on the top, rather than rough sandpaper have been used.

I'd sand that heel flat, rather than try and use shims. And look to see if the neck is level withy reference to the top of the guitar when fitted. Often the fretboard isn't quite an even thickness from side to side to compensate. If it is flat, then leave the side-to-side angle well alone. Also remember that the sides of the pocket will stop the neck rotating even if you level up the side-to-side angle, so you'll also need to attack the pocket sides and use some veneer fillers to allow the neck to sit fully perpendicular.

I'd try a hot iron and a wet cloth on the veneer and see if those marks will steam out. Most should, and it will at least look a lot better, if not perfect.