Star within a star within star within a star........

I have been thinking about this design for simply ages. I may or may not have feathers on the outermost star. I'm having a problem with the mechanics of the design. In theory this shaped star should fit within an octagon of any size, but as you can see the perfect octagon degenerates as it gets smaller. I've tried designing it from the smallest out and there is still distortion. The basic star itself is probably my favourite block, I love the secondary star of the white triangles.
The design problem happens in exactly the same way whether drawn out full sized on paper or drawn in Quilt Pro. I've been told the problems with the computer is there is a rounding up or down and the drawing on a drawing board is a similar effect.