I would say the scraper is your problem... on pens a scraper does not seem to leave as fine a surface as it will on a bowl... especially on acrylics and plastics... I would assume you are getting a rippled surface... if you have not learned to use a skew properly, I would suggest staying a bit proud of the bushings and sanding your way to the final dimension and then going to MicroMesh.. wet sanding to 12000