Gundogan gave an acceptance on his share of the blame after Premier League leaders Man City failed to beat the relegation Leeds by a scoreline on Saturday.
The midfielder scored both goals as they maintained their title charge with a 2-1 at the Etihad Stadium but his late missed penalty opened the door for a potential Leeds fightback.
Regular penalty-taker and top scorer Haaland passed up the chance to score from the spot to allow club captain Gundogan a shot at a first career hat-trick, but things almost went badly wrong.
Gundogan’s effort in the 84th minute proved to the post and Leeds scored just moments later through Rodrigo.
Suddenly, the game City had completely dominated until that point ended in a frantic finish but the hosts held on.
Manager Guardiola was far from impressed by the episode and Gundogan held his hands up.
“It was a good performance,” Gundogan says: “Unfortunately, we weren’t able to transmit that performance into the result.
“It feels like this game should have been won by at least three goals difference.
“We had a lot of possession, we were able to create a lot of chances. The negative is that we were not able to score a third one.
“The game could have been over in the first half and, of course, also in the second. We had plenty of chances — myself included, unfortunately — to score a third one.
“Conceding quite an easy goal made the last five to 10 minutes a little bit nervous for us, which should not have happened. It’s another experience that we take on board.”
That incident aside, Gundogan was outstanding, putting his side in command by sweeping home from Riyad Mahrez’s passes on the edge of the area in the 19th and 27th minutes.
City could have increased their lead several times over with Haaland going close on many occasions, including hitting the woodwork twice himself.
Gundogan feels it is important City, who now face Real Madrid in the Champions League semi-finals on Tuesday, which continues to set high standards as they chase the treble.
He said: “Some people say it is more important to win than to play well, which can be true. But I think that’s not our standard.
“Of course, we want to win games but also we want to keep playing the way we have done here.
“There’s just a few games left until the season is over and every game is like a final right now.”