Lewandowski replaced Sami Hyypia - with whom he shared managerial duties last term - earlier this month following the Finn's sacking after a poor run of form put Leverkusen in danger of missing out on UEFA Champions League qualification.
But despite overseeing a victory over Hertha in his first game in charge, Lewandowski said there is plenty more to come from his team.
"We still have much work to make our game more stable," he told Bild.
"We have some areas to build on, no question.
"I was quickly back in my element (on Saturday). I know the team and the situation."
It looks increasingly likely that fourth-placed Leverkusen will need to qualify for the 2014-15 Champions League, having seen Schalke overtake them and move seven points clear in third.
