Jill, have it slabbed, that way it will be sealed straight and no one will ever know it is warped! (yes, humor)

I straightened records in college, using a 100 watt light bulb, right in the lamp, just remove the shade to make it easier. lol But you can gently heat the card and get it straight. Have a big dictionary or large book, so use for a press when cooling.

Someone add this to the no cleaning pledge. "I will not straighten warped slot cards..."

One more siggestion. Do you have any kids? Maybe some in the neighborhood? Get a clothes pin, clip the card on the back wheel of a bike so it hits the spokes. Cool motor sounds. Now that's what to do with the warped slot card!