The U's will go into the final game of the season at Carlisle next Saturday three points above the relegation zone, following fourth-bottom Scunthorpe's win at MK Dons.
Dunne said: "We're staring relegation in the face.
"It's a big week where you can either be a League Two player and disappear or a League One player and push on.
"It shouldn't go down to the last day of the season. I'm furious. We were lacklustre and let fear get in the way of everything.
"There was a big crowd and we were booed at the end and rightly so. We gave the fans nothing to cheer about.
"We had two or three opportunities, but there was desperation about our play and the whole game.
"It looked like we were waiting on MK Dons to do us a favour (against Scunthorpe), which they didn't.
"It's been in our hands for the last three games and we've picked up one point.
"Now it comes down to the last game at Carlisle, which isn't in our advantage. We have to give a better account because there are a lot of jobs on the line."