Mustafi struck in the second-leg as they reached the final 16.
He said: "Playing at home is different when you lose the first leg 1-0 away. We knew to had to score but at the same time not concede, and we managed it well.
"We started well and wanted to play forward. We had a lot of opportunities and the goals came from set-pieces, which is something we work on so it's good that it pays off.
"We're trying to produce on the pitch what we're doing on the training ground and the manager encourages us to stick with our style of play. We have to believe in ourselves and it will pay off."
On Laurent Koscielny's injury, he added: "I hope it's nothing serious. He had a smile on his face when he came off."