Ah, Houston Mission Control, we have a problem.......top of your guitar is curved, not flat so part of the above explanation might not work. Even Micro mesh pads can build up with crud and easily add scratches before you notice however if in the direction of the grain they may not be so noticeable whereas across the grain they would possibly stand out.

The size of the sanding block sounds huge as a standard cork ones are 110mm x 60mm x 30mm and the guitar kit micro mesh pads as per this link are 2" X 2" ... https://www.thesandpaperman.com.au/s...keep_https=yes and they are much easier to work in tight curves such as on a lower cutaway on LP's.