Can you trim out the lines by making the cockpit a little bigger?

: Help! I did a bad-bad thing. I made some lines on the deck of my thin veneer
: boat to aid cutting out the cockpit-now I can't git rid of the black magic
: marker lines-I have tried sanding-acetone-lacquer thinner etc. but still
: can see the lines..would have LIKED to finish deck natural..any and all
: ideas appreciated.