wrong change at paul

Went to takashimaya in Futagotamagawa, we planned to eat sandwich at the river so bought 3 sandwiches and 1 sweat at Paul. it was about 2000 yen in total. and i gave her 10000 yen. However, i realized later that she had given me back 9000 yen for the change. I did not go back there and felt guilty.