Step 4: primer
The next step was to apply a primer over the patch.
I used a self etching, sandable primer, and followed the instructions on the can. I taped over the edges while I was working. Once I was done, I used a 600 grit sandpaper to soften the edge of the primer, and roughen the surrounding paint.
That's me sanding. Photo by my wonderful husband, who was not at all worried about his wife attempting auto body repair. ; )
Hand sanding takes a bit of extra time, but allowed me extra control. Here you can see that I made sure to get the primer up under the lip of the plastic. I also kept tape and newspaper over the lower (plastic) fender, as I didn't want to scratch that up while sanding the bottom edge of the metal fender.