sprayed my rear bumper (fiberglass) with a low gloss black enamel and it came out way too shiny. Cause?? Fix??

If you used spray cans try holding the can farther away and spray more of a dry coat or spray a satin clear last. If a mixed paint, take it back and have them mix in more flattening agent. It could be trial and error to get the exact sheen your looking for.

If you used hardener it will generally turn out shiny. If it's spray cans, use the above advice and don't paint it in the sun.

not a spray can. tried the Valspar implement enamel. did not use any hardener. thought the enamel would be a one shot deal and be done with it. now have a mess as in can't shoot anything else over the enamel.

Valspar tractor paint, like from TSC ? Find a small can of Valspar or any of the tractor enamels in flat black and mix in and recoat. Start with a small amount and test on something first. I've done this with regular paints with good results.

It will dye back more with time. You can rub over it with a Magic Eraser to take some shine off.

Brad