The ex-Rangers midfielder will face his former club in a Premier Sports Cup last 16 tie on Friday evening and is fully aware of the size of the task facing the Championship men.
After going down to a 3-0 defeat on home turf to Thistle, the 34-year-old former Scotland international knows major improvement will be required to avoid a hiding.
"We got what we deserved out the game,” he said. “I thought we were poor from start to finish but we've got to bounce back quickly because it doesn't get any easier in the next couple of weeks.
"[Rangers] are league champions so we know how difficult a game that's going to be, but we'll go again on Monday and work on a game-plan. It has to be better than Saturday that's for sure.
"It will be a different challenge, but every game brings a little bit of pressure. They'll be favourites but if we go out and perform like that it will be a long night for us."
Headers from Ross Docherty and Kevin Holt and a Ross Graham own goal did the damage for Dunfermline.
Dorrans added: "[Partick] were first to every ball, they wanted it more than us. It was just very disappointing from the first whistle.
"Everyone in there is thoroughly disappointed so we need to work on it to put things right.
"We know that’s not acceptable what we just put on there for 90 minutes.
"Everyone's got a point to prove going forward."