I've just the top left corner to finish. Demeter or Kilgore - could you explain 15 across DITONE. I see the definition at the end but I'm not sure how the rest of the clue works. Thanks.
31d is amended; for 31a, the wordplay is an anagram (ploughed up is the indicator); solving that anagram should indicate that 31a is also amended and I think will guide you to 31d pretty easily.
As for the extra letters, you should have 10 in total; 8 of yours are correct but you have an extraneous L.