What is the right course of action now?

In Germany, the "Rechtsfahrgebot" requires all drivers to use the rightmost lane on highways unless they are overtaking another vehicle or avoiding an obstacle. You should only stay in the middle or left lane while actively passing slower traffic or if the right lane is too congested to safely merge. Once you have completed your overtaking maneuver and there is enough space ahead in the right lane, you must return to it. Staying unnecessarily in the middle or left lanes is not allowed and can lead to traffic disruptions or fines. In this scenario, remaining in the middle lane was correct as you were in the process of overtaking. After you have finished overtaking and ensured it is safe, you should return to the right lane. This rule helps keep traffic flowing smoothly and reduces the risk of dangerous situations on the Autobahn.