"We put enough balls into their box, enough to win," Cotterill told reporters after the game at Ashton Gate. "They've scored from a bad throw and bad marking at a corner.
"Sam Baldock hit the post, we've had enough balls go right across their box. We've got to be scoring those chances. We've got to be more ruthless.
"I'm not going to use the conditions as an excuse. The frustration is we're having to chase games. We're having to make too many changes. Maybe we have to change things now."
City are back in action on Saturday afternoon when they travel to Oldham.