Summary

Let me say first that this can be resized to fit the F1.  Make it within the confines of a 109mm x 109mm rectangle and chop the corners off a bit.   I have included the Lightburn file depicted and also one which fits in the bottom plate recess of the xTool F1.

This is simple as can be.  Make some 12mm x 20mm boxes and cut through 3mm basswood or plywood.  Then take your perimeter and make just a rectangle.  Glue the two pieces together. 

Don't buy templates.  Scratch your head, look at the problem and solve it.