The 1-0 Wembley loss was England's last friendly before the start of the Euros.
Asked if it will hit the players' confidence, Mainoo said: "Not at all! We know the quality we have in the changing room and now we just have to show the fans we’re good enough and we can compete in Germany.
"I think going into a tournament after a loss can be a good thing. We’ve got a point to prove now to ourselves really because we know we’re better than that and play a lot better football.
"It was humbling and we have to come together now. We’ve got a chip on our shoulder and have to come together and have the motivation now to go into that first game and prove a point.
"I think so if we’re not winning we’re learning. Any chance to learn is a good opportunity and better now than in nine days."