That is pretty exciting-but I definitely understand that it’s stressful as you’re dealing with firm deadlines.
Unless you have done this already, do you think it would help to give them a bulleted list with your strengths and contributions to the class? They probably have so much swimming in their head at the moment so this might help give them some structure. But maybe you should also consider giving them an out-something like “I know you are probably busier than you’ve ever been, and I don’t want to add onto your load. Would you prefer I ask someone else? I appreciate your willingness and I hope you’re having a great experience on the campaign” or something like that. Then you’re still on good terms, and who knows, maybe they’ll be able to do it after all. Good luck.