Whenever I try to inset the faces like you did at 11:50, the faces distort. I’m copying everything you’re doing, so is it something to do with me using a newer version of blender or a setting I have?
Yes, that has all the signs of a scale not applied. You can select your object and with N ou can call the N panel to see the scale of your object and it’s probably not 1, 1, 1