Don't use filler at all on scratches ! It's not a dent .
Sand with 800grit wet with washing up liquid to lubricate . Use a block of wood or a rubber sanding block until u can no long feel the scratch with a finger nail . Prime as normal , wet flat again then it's ready for paint .
When you prime the area , DONT paint upto masking tape , u will be left with a hard edge that's a pain to get rid of . Use a grey scotchbrite pad to key the area and dust it on .