If I were you I would just go back and pay.

I was at the local Napa today to get an airfilter, and told the guy
that I owed the store $1.26 for a couple of plastic license plate nuts
and machine screws. He remembered the transaction, said thanks for
coming back to pay, and looked genuinely pleased to have had me come
in. That's just gravy for me. The real payoff is the satisfaction and
peace of mind I get from doing the right thing.

JP
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The soapbox is yours.