How do I calculate the correct side gusset dimensions to match my main panel?

Hey guys so I am making a leather bag for my GF, and I really want to do this one. However in the youtube video where it provides the pattern, one of the side gussets or panels, looks smaller on the pattern than the video itself. I was about to cut the leather in the shapes, but that really tripped me out. Can anyone help me figure out the size or maybe another template because I really want to do this bag. Any help would be wonderful.

Video: https://www.youtube.com/watch?v=fiJvV6igcMs
Time Stamp of side panel: 1:37
Pattern: https://drive.google.com/file/d/1KZRp6KHOAOpZEJJENbtGpvc8oe33cU_a/view?pli=1