"Schalke's win today was undoubtedly deserved," Hecking told reporters after the match on Saturday.
"We lacked consistency, especially at the back. It wasn't what we had imagined for ourselves.
"We didn't show the necessary compactness or discipline on the day to be able to compete with a strong side like Schalke. Our focus now needs to turn to the teams below us in the table."
Wolfsburg are currently just a place and six points above the relegation zone.