A crowd forgets plenty of polished bits. The moment you went off script is what they talk about after.

Polish is admirable and forgettable, because it goes exactly the way everyone expected. What sticks is the unrepeatable thing: the recovery, the joke nobody planned, the moment you were visibly present rather than performing. People remember feeling something, and surprise is one of the quickest routes there. None of that makes preparation wasted, since preparation is what gives you room to leave the script safely.

Prepare well enough that you can afford one unplanned moment, then take it. A question for the audience, a change in the last chorus, a true aside. Afterwards, ask one person what they remember and listen to the answer.