4842 Final Step

[NobleRoman]

Completed clues, got message and instructions but 43 cells is defeating me.  I understand the parts of the message referred to but that would be 46 cells

[ProfessorMaisie]

You should only have 43 cells highlighted - 30 of them produce a very obvious symmetrical shape and the others, although appearing to be random, are in their correct positions because the full image (as shown in the wiki article) has been cropped.

Your 3 surplus letters will not match any specific points in the diagram and must be answer/grid errors.