Angela Walters would say what other here have: repeat what you call a mistake and it looks like you did it on purpose.
Did you try drawing the quilting pattern on paper first? Best thing is to get the largest, cheapest sketch pad you can find, and use a marker. I'd try starting in the center, making a triangle that has the same angles as your piece. See where you can travel from there. But seriously, repeats of anything look intentional. Don't sweat it.