The Chairboys were nowhere near their best and fell behind to a John Mousinho goal two minutes into the second half.
Scott Laird was dismissed for the visitors in the 65th minute but Wycombe could not produce the comeback that would have moved them into second place in npower League Two.
Waddock commented: "We've not been good enough recently at all. I can't take anything away from Stevenage - they set their stall out to defend but we have to be good enough to be able to cope with that and we didn't.
"Their keeper hasn't made a single save and Nikki Bull has ended up making several and that's been the same story for too long and we've got to improve in front of goal.
"I just told the boys in the changing room that the performance simply wasn't good enough. People will talk about fatigue but fatigue is not an excuse."
Source: PA
Source: PA