The simplest way, for now, to return to the original start position, is to use the Direction button and go East if you were going West initially (and vice versa), and Start a new PA. I do that once in a while to verify and refine my PA, if needed.

It also happens to me, once in a while, that I mistakenly hit the Start button right after having performed a PA, somewhat frustrating but I always have the choice of not performing the adjustments if the PA is fine.