Tech69 is giving you good advice. If there are sand scratches remaining after the initial buff, more than likely you did not cut it enough with the last color sand. You need to go back and re-color sand that area and then buff again. The whole cut and buff process is a matter of progressively going to finer and finer imperfections IE orange peal, sand scratches, nibs etc. You can't sucessfully go to the next step until the previous one is performed successfully.
Good luck and keep us posted.