Thanks NAC, ProfessorM and Toorak.
I now have the message from extra letters, instructions on 18 cells and one poet.
Have not filled the perimeter as too many blank cells.(20?)
Trying to find the second poet.
The last word coming up in column 1 is 7 letters ending in ED.
But the space provided is 6 cells so ED can become S. But that would be changing the line in the poem.