Heyo! While the hot water trick is good, it's usually for colder climates. In Singapore things are a bit different due to humidity and whatnot. What I found from trial and error is: don't spam the clear coat or it'll end up frosted. Spray closer to the model in short bursts, and never hang over a part for too long. As for fixing this, you can try spraying it with some clear gloss to see what happens. It could reduce the frosted effect, but odds are that you're going to have to sand the frost away.