Demeter, you need to double-check your work very methodically. You've either got a wrong entry in the new NW quadrant or you've miscounted letters. KIDDOS is not relevant because it's not one of the original entries, but the letter is still K because the original begins with K, as you said.
The initial letters of all the original entries, ignoring those from unpaired clues (which the second instruction, confusingly, fails to tell us) are used to fill the new 6x6 NW quadrant. There is an exact match if you complete 11dn correctly.
If you cannot get an exact match then one of your new entries in the NW is wrong or one of your original answers is wrong.