68 barracuda 383s "Driver Paint Resto"

I'd dig it all out. You can apply a little heat to it with a propane torch, and it will scrape right off with a putty wrench or gasket scraper. When you got it off that fender, you may have noticed some surface rust on the fender, under the filler. That's why you spray the epoxy primer, and do your filler over the epoxy. When the filler starts setting up, the chemical reaction causes it to heat up. I'm talking....almost burn your hand hot! That heat creates condensation between the filler and the cooler bare metal. It can't escape....and causes the surface rust, which can eventually make the filler turn loose. Filler on top of epoxy bonds to the epoxy, but can't cause the flash rust because the epoxy has the metal sealed. If it was hit early in life, the filler nowadays is WAY better than the best thing available back then. I like Evercoat Rage Gold. Just keep working it until you get it straight. It will take several applications of filler, and plenty of sanding with a long board...but you'll get it.