Adding letters after a challenge

My husband put the word varmint down where the M was already on the board. I questioned the spelling and we agreed on a friendly challenge. He was right. As I was about to ask his points, he puts the letter S down making it plural and now having used his seven letters. Since I challenged with the six letters he put down, can he just add another and get credit.

This is why it is a good idea to agree before a game on how a player will indicate that they have finished playing their word. In Scrabble tournaments, for example, once a player announces their score, they cannot change their play.

In your case, even though you didn't have such a rule in place, a player is never allowed to change their play after a challenge has taken place. So I'm afraid you've been duped ;-)

Hope that answers your question,