Thanks guys, I've had a closer look at what I was doing and it's clear that the temp was too low for the hardener and I was pressing the plastic squeegee too hard against the rough surface. Problem is that I was fibreglassing during the very warm afternoons but tried applying the fill coat in the cool morning. I've got some short foam rollers and foam brushes. As soon as the weather clears (saturday according to the forecast) I'll get out and try again. I'll take the opportunity to give it a good scrub with steel wool and wash off the blush.

Thanks all.
Bohdan