Hmm, sounds like you may have.
I find if i DO over cook a screen, i can get it out with high pressure.
I would go to Home Depot, and buy a 500 w halogen light for 12$,
Place this 13" above the screen. Turn light on for 12 minutes.
Should work great.
ALSO, double up your artwork on the transperencies. That is print two, and line em up and tape em. you will see a difference when you hold it up to a light. WAY darker. this lets less light thru, giving you a better image.
Hope this helps!