You could perhaps change the challenge slide to stipulate that we are to create a public class before going into the challenge. Especially for people like me that saw you made your class public, paused the video, spent 20 minutes working out how to delete that class, recreating TankPlayerController as public, hitting play… and being told that it doesn’t really matter! Doh! 
I’ll second this. I tried to go back and make the change after and managed to corrupt my files quite badly. Took me forever to get everything back up and working again.