Surprise defeats for title rivals Marseille and Lyon had given the champions an opportunity to reclaim top spot with victory at the Stade Louis II.
However, despite having the better of the chances, Laurent Blanc's side failed to find the breakthrough against a stubborn Monaco defence.
Van der Wiel felt his side lacked the necessary poise in the crucial moments, yet he remains positive about PSG's chances of retaining the title.
"At this level, you have to kill the matches," the Netherlands international told France Football.
"We had many opportunities, we were solid defensively, we had possession, but this kind of game is played on the details.
"Obviously, we're disappointed because we had the opportunity to take the lead of the championship. But we remain confident. There are still a lot of matches to play before the end of the season."
PSG and Monaco meet again on Wednesday at the Parc de Princes in the quarter-final of the Coupe de France.