Yes, something odd there, with all the grid stuff off, mine is still snapping to a grid of some kind (or is just plain wrong). Looks like a Fritzing bug. It may be round off error in floating point, although mine is off further than yours seems to be. For me setting 21.275 changes to 21.257 I can get closer by moving to px, but this isn’t right. In the big picture though, it is close enough I expect, we won’t notice .02 mm difference (as long as it doesn’t accumulate across the board which it should not).
OK here are two sketches with complete boards for left hand and right hand. Major changes: double the connectors so you can connect 2 wires to either board for the shared wires from the mega, added a ground and a bypass capacitor (may not be needed but available if it is), tightened up the routing to make space for the second connector. It would be best if you switched to the left hand sketch to make your changes, but since they are currently identical it shouldn’t matter. Technically these two boards will work as is, but the routing is only rough (although correct) as it will change if the sensors move.
new left hand board (the same as the right with pin numbers changed at present):
accordion-left-hand-Sketch.fzz (178.6 KB)
and an updated version of the right hand sketch:
accordion-right-hand-Sketch.fzz (178.6 KB)