Relax, take a breath.

Yes foil or foil tape on the screen is a very common practice. A number of other materials can be used as well.

A word of caution about placing damp towels on the screen. If its a metal screen the wet towel will cause it to start rusting.

As for a emergency fix its not really needed. One night is a drop in the bucket as humidity is something that needs to be sustained to have a seen effect be it bad or good and one night is not going to cause that. Not in this situation.

Now there is a very easy fix. I use a 40gal glass tank with a foil tape covered lid for my BP. Why? Because I like the way it looks. Is it easy? Maybe not as easy as a pvc cage but I find it easy enough. In my tank the humidity stays in the 30s so to fix this issue I place damp moss in both hides. This creates a micro climate inside the hides and since that's where your snake will remain most of the time it will directly benefit from it. It does not matter that the outside humidity is low as long as you are providing the moss.

During a shed I keep the moss damp throughout the process but during regular periods I make the moss damp and then allow it to dry before making it damp again. This mixed with a daily mist should keep your snake happy and give you perfect sheds.

Cypress mulch is also a great substrate for low humidity cages and misting, even heavy misting is unlikely to cause mold as long as you have proper air flow. This is created by leaving an area of the lid open be if for a heat lamp or just for air flow. Just avoid covering the entire lid.

Also being new here start to use the search feature and you will find most if not all of your questions can be answered without having to wait on use to chime in.