Iris, that's a lot of questions you have!! Let's see if we can get a few of them answered anyway. You ask why can't you use Jell-O? Because it's full of sugar and that won't work. If you go back and read through this entire thread you'll see some of the issues people have had with it.
The curling is good. Often when I make butterflies they have curled up and popped off the veining sheet the next morning. When they are dry they have some flexibility, so you can pinch the center to give the wings dimension. Trim the edges to get the ragged edges off.
Two hours is not nearly long enough to leave it. You are better off letting it set overnight. Refrigerating won't help at all. You cannot speed up this process. You will figure out through trial and error how to make it "not to thin, not too thick." You do want to watch out for air bubbles in your painting -- there's nothing worse than a butterfly wing with a big hole in it!
When making red, add 1 drop of airbrush red color and if that's not dark enough add another. Airbrush color is very liquidy and works better in the gelatin solution. You can also LIGHTLY sprinkle some disco dust onto the wet wings to give them a little sparkle as they dry, then do up the edges with a thicker coat of disco dust when you're done.
Hope that helps!! It would help some if you could post pix of the problem wings so we can better get an idea of what's going on. Good luck!