Unfortunately design help is outside the scope of Problem’s and Support so I’m going to move this post to Everything Else.
That said, I can share a mini-tutorial for my own method of creating stitching holes in leather from another thread: The overnight bag of 1,000+ stitching holes
If you need to get into the corners using the method described in that post, you’ll need to slightly increase the length of two of the lines (parallel to each other) to have their ending holes in the corner, but I’ve found it to be effective enough for my own needs.