You did not supply enough information regarding the depth of the scratch, color of the bike etc. If the scratch can be felt with your finger nail... then it is most likely to deep to buff for sure and probably to deep to color sand. But that would be the first two things to try, touching up.. not a good deal unless you are very experienced in preparing the scratch (actually making it deep enough to get color and clear back up just above level of surrounding paint) then sanding level and buffing to shine/remove the sand scratches. Not a simple thing to fix scratches, nor quick. Go to a high end collision shop and ask them, not a small body shop or a back yard of a someone a friend knows who paints cars at night.