The Dutchman has admitted that the reigning German champions are not on top of their game yet, while Philipp Lahm insists a winning start to the season was vital
Goals from Robben and Mario Mandzukic gifted Bayern an early two-goal lead, before an own goal from Dante gave Gladbach a foothold in the opening match of the 2013-14 Bundesliga campaign.
Although David Alaba put the match to bed after the interval when he converted a penalty, Robben was not entirely satisfied with his side's performance.
"We need a little more time. We're not where we want to be, but it was enough against Gladbach," the 29-year-old told the club's official website.
"We're still working on the little things. We'll keep getting better over the next few weeks.
"The most important thing is always to dominate play and attack aggressively. We did that well at times and put our opponents under pressure."
Meanwhile, captain Philipp Lahm was pleased with his side's winning start to the new campaign after a mixed pre-season under new boss Pep Guardiola.
"What matters is to win the first game of the season, so that’s a good start," the defender said.
"After we conceded an unlucky goal, the momentum was with our opponents. But we’re pleased to get into the season after 45 days preparing for it."