the dimpling isnt a result of over tightening, but rather because your screws are too long. the bottom of your board is the base, not a hard surface so the screws arent going to bottom out and stop turning. get shorter screws and "keep turning and turning" until you rip your inserts right out of your board or stop going he-man on the board and adjust them until they are snug, not tight..
its a snowboard, not a car.
the dimples should push back down once the screws are backed off and the board is ridden. worste case scenerion the screws can punch a hole and crack your base.