First thing to do is use something to remove the anti- bonding agent used to prevent the part from sticking to the mold during the manufacturing process. I.e. if wax was used a wax remover should be used. By sanding first you are just pushing the wax around and into the scratches.
Jeff, do you only rely on soap & water for composites?
Every surface i prime or paint gets a final “wash” with a prep solvent specifically targeting wax, oil, & silicone. Cheap insurance.
I happen to have Matrix MX9000 on hand. I’m sure every paint system has an equivalent product.
BP