Having hammered the Belgians 5-0 two weeks ago, the Ligue 1 champions stuttered to a 1-1 draw at Parc des Princes in Group C, meaning that they will now have to wait until their next match to seal their place in the knockout stages.
"We hoped to win and get all three points," Motta told PSG's website. "Anderlecht pushed us around a little and we couldn't find a way through their defence.
"No match is ever like another, so obviously it was different to the first leg. Nothing is ever easy, especially in the Champions League. Now we have to fix the mistakes we made."
PSG host Nice in Ligue 1 on Saturday.