I assume you didn't clear to lock in the original artwork before you started touching up? You "might" be able to recover some of the artwork regardless (at least partial artwork as a guide) if you sand very carefully. Another option: scan the entire playfield as is, trace it into vector artwork, and create layered masks.
Honestly, most playfield touchups I've done are on EM's and I've had good luck with water-based polyurethane (doesn't smell either):