No worries Toshi that headstock round top looks much better now ! I have been a draftsperson for over 25 years so I can spot a circle and spot one that's not !
Neck sanding plans sound good, see if you can slip 180 grit in there so 120, 180, 240, 320, then your decal, then clear lacquer

good luck buddy !

if we had to vote for sander of the year (SOTY) I think I would be voting you haha its all worth it once you see the finished product