Hot Rod Flatz paint problem
 

I applied 3 coats of Hot Rod Flatz, Flat Black, and found that it dried with some spots that remained glossy. Did not flatten out properly.
The paint was well mixed with the correct proportions of paint/hardner/reducer. I made all attempts to apply at a uniform distance and right angle. I 'm lost for a cure.
I have been told that a light sanding with a wet scuff pad will even things out and look OK. Has anyone ever tried this remedy?
Any help would be greatly appreciated,
Bob

Did you apply a full coat sealer before applying the topcoat?

I've seen this happen with differing substrate materials before...