The Bati thrashed the United States 58-12 in their tournament opener last weekend and face a Welsh team on Sunday that conceded 50 points against Papua New Guinea in Port Moresby.
Despite scoring 11 tries, Potter said Fiji let in a couple that were preventable.
"We were just a little bit quick in our defence - we didn't make effective tackles and they probably could have had another try as well, just a guys stepped from outside the field of play to catch a ball," he said.
"So we got off lightly there with our last plays, we've got to make sure that we don't walk when the ball is in transit, as far as in a kick.
"Everyone's got a job when the ball is being kicked to help their catcher or to be in the vicinity to make a tackle if something does go wrong".
Photo: NRL Photos The Fiji Bati World Cup squad