They were made to pay for their profligacy when Kevin Gall equalised for the hosts midway through the second half.
"We should have won. We need that ruthless streak to take more of our chances and see games out once we are in front," said Allen. "There's a massive tinge of disappointment that we didn't win. The players know they should have put that game to bed."
Allen hailed striker Richards for his goal, and believes his side can build on their performance in the north east.
He added: "Richards deserved his goal and could have had three. He has pace and desire and it's great to have a player performing like that. There is loads of desire and energy in this side and there is plenty that we can build on as the season progresses."