The Wallabies ran out 20-14 winners, but England had a number of opportunites to reduce and even overturn the deficit.
Captain Chris Robshaw came in for criticism for deciding to go for tries from penalties instead of taking the three points, but Ashton believes that he was right to make such decisions and that it was the final pass that let England down.
"I think we cost ourselves the game. We had enough possession in their 22 and we just didn't take our chances," Ashton said.
"I think the right decisions were made from those penalties. I thought we had them but we just couldn't find that finishing pass. Toby Flood tried to find me through the back and if the pass had gone to hand I would have been through a hole. And then Thomas Waldrom dropped the ball over the line.
"You have to take your chances. Our attack was better (than it was in last weekend's 54-12 win over Fiji) but we are lacking that clinical edge. We put ourselves in a position to win that game and that was the frustrating thing."
England will be looking to bounce back from this defeat against South Africa and New Zealand in the remaining autumn internationals.