This makes for a super easy cut if you have a 12x24 mat. I just sized the width at 23" and put two pieces of paper side by side so I would only have to load once.
Then I scored at the obvious places (sorry, I forgot a pic - I'm horrible at this tute stuff).
So EASY! And boy am I loving easy these days. Here is a lovely new cut file for your overcrowded computer filing system (and one without slots if you don't need them):