Hi guys,
Been skinning for quite a while but now I've stumbled onto something new. I was doing a pair of doorsills using 400 gsm cloth. I applied the first coat letting it go to a full cure and then applied the 2nd coat ( epoxy laminating resin + fast type hardner) with sanding cause I felt the first layer may have been too thin.

2nd coat went for a full cure and then I started wetsanding it ( 400 grid ) After getting it all even, I saw white marks all over the panels, nothing new but this time they remain visible :-( Wiped it down with acetone but even then I can still see them .. Do I need to sand down even more or did something go wrong here ? Please advise :-)