If you have a sharp wood chisel, you can use it as a scraper to remove the varnish inside the "tape box." It will go much faster than sanding and get the whole area clean of varnish.

Then use the sandpaper to rough up the area. You only have toget most of the area roughed up. The varnish is all gone.

You will be happier with the wood pieces if you cut them on a 45 degree angle, assuming you have a miter box. You will need a little more half-round, but it is readily available or Pygmy will send you another stick if you ask them.