You are probably way beyond any recoat window for that epoxy so you get to sand it in order to get any new material to stick..While you are doing that just remember to be glad that you do not have to go through the rust removal deal again.
We generally recommend that one shoots another coat of epoxy then do your fill and blocking. They way I do it is to shoot a coat of 2K in a different color than the gray that you used and block and long board on that coat..that will tell the tale as to where you need to put on a bit of fill...then block the filled areas and shoot some more 2K and block and longboard again..just keep doing that over and over until all the wrinkles are taken care of..
Next step is to shoot either a tintable sealer or the appropriate seal coat of epoxy in the color you need and apply the base coat then of course the clear..all the way along I do what I call a check sand which is a real lite scuffing to expose any trash or flow indicators I might have..If you repair any foo-bahs as you go the end result will be something you can be proud of..
I have tried most all of it and now do what is known to work..