I knew it was the wrong product, I even took care not to adhere it too firmly. I also knew I had low tack painters tape somewhere but couldn't find it at the time (got it now, but hopefully I have done the job correctly).

I know what you mean about the filings! What a mess... I was kind of loosley following the fret levelling post on this forum, which uses the steel wool.

Board cleaned up super easy with very few passes of a fine grit, and the neck now has its first coat of tru-oil applied. One small run on the headstock, at the corner nearest the low E peg, collected on the face side and soaked in leaving a dark patch I couldn't move. Will see how it goes in a few coats. (I thought the tru-oil would smell a bit better, hopefully most of that is the solvent and it will clear up as it cures?)