Hello, I know it’s probably a bit late, but I ran into the same problem and figured it out. At the beggining of the class, Jonathan selected the sphere at the center and resized the UV, before puting it aside and hiding it. The heatmap is calculated accordingly to every mesh data in the object. If you simply hide the sphere at the center without resizing, Blender will calculate the stretching based on other faces in the same objetc (even those that are hidden) and you will get a lot of stretching. What I did was: I selected the sphere and then unwrapped that, and it got really ugly, but the streching was gone and I could finally hide the sphere.
