I’d say you’re fucked. Best thing I can come up is fake being sick and hope there’s another try available in a few weeks. And use that time to prepare. In proper maths, it doesn’t really if they test your knowledge or calculation skills… Both requires you to learn.
Concerning the cheating: Entirely depends on the situation. Usually there are people watching and making sure no one cheats… They might have seen some attempts and be better at spotting it than you are doing it if it’s your first rodeo. I wouldn’t try unless it’s a single 65 yo dude who doesn’t care.