Simon McIntyre scored the only try of the game as Wasps defeated the Warriors 10-6 on Sunday at Adams Park.
While his side came away with the win, Youngs believes that Wasps didn't play well enough.
"We showed a lot of heart and a lot of determination in the last four minutes to keep them out but we shouldn't have been in that position," said Youngs.
"Our ball retention in the green zone and the strike zone was really poor, I thought our kicking game we came second best, they out kicked us when they needed to out kick us.
"And certainly in the second half our set piece fell apart. The scum fell apart and the lineout was nowhere near as solid and then you end up defending for big periods."
Wasps host Newport Gwent Dragons in the Amlin Challenge Cup on Saturday.