Gomarsall opted to try to force his way through rather than release the ball to fly half Chris Malone, who was perfectly placed for a strike at goal, but ran into a team-mate.
"Gomars has said it should have gone. He's held his hands up," said Dean Richards, the Harlequins director of rugby.
"At the end we should have just dropped the goal. You couldn't have asked for a better position."
Richards admitted he was "very disappointed" that his side failed to win a match they dominated in the first half at The Stoop.
"We had 70 per cent of the lineout possession, our scrum was pretty good and from a territorial point of view it was probably 60-40 - but we didn't capitalise on it," he said.
Harlequins have only two points from their opening two matches in Pool Three, which also includes French side Stade Francais and Bristol, and Richards added: "We have got to win the rest - it's as simple as that.
But he described the home clash with Stade Francais, along with two matches against Bristol and the return in Cardiff as "all winnable".
By contrast, Dai Young, the Cardiff director of rugby, is happy with a win and a draw from the opening two matches.
"It wasn't perfect but it's seven points out of 10 and that's a match they could have won. We weren't really in the game for the first 25 minutes.
"There was a lot riding on it and I don't think either side played to their potential."
His side's next Heineken Cup match is against Stade Francais in Paris on December 9 and Young admitted: "We are going to have to be better than we were today."