Help From The Community

Unfortunately it is difficult to match panel/gussets to your pattern in real life unless you stick to a specific type of leather and thickness that works with that particular pattern. You may have it mathematically correct, however, if you change the thickness of the leather, use leather that is softer or more firm, or you stretch/compress the leather more around the corners, your dimensions can be wildly off, even on a small bag.

Trial and error using similar materials to make prototypes works well, then you can transfer these measurements onto a pattern.