You have to patch the hole first. (think I mentioned that) Once you patch it with a small piece of metal then you can start laying bondo over it and working it. There are tools used to cut down bondo quickly but some 36 grit paper will suit you just fine. Get it down with the 36, go to some 80 or so to get it closer to what you want and to get the marks from the 36 out. From there i would use 240 or 320 to get a "smoother" finish so you can primer it. Sand the primer with some 400 and look it ever real good to make sure it's what you want... Then seal it, prime it, top coat it, and clear it.