The Frenchman was disconsolate after Sunday's shock defeat saw Juventus retain their Serie A title without kicking a ball
Francesco Totti pulled a goal back after Mariano Julio Izco struck twice in the early stages, but in the second half Gonzalo Bergessio and Pablo Barrientos rounded off a stunning victory.
The result means leaders Juve have secured a third straight league success and Garcia said everyone at the club had to take responsibility for a disappointing afternoon.
He told reporters after the game: "We all made mistakes today, myself and the players. There was a difference in motivation.
"This defeat doesn’t cancel out the great season we’ve had, but we have to end it differently. We’ll work hard after this loss. There’s a big game on Sunday against Juve and we can’t make any more mistakes."
Roma captain Francesco Totti then called upon his team-mates to use their promising campaign as a building block for success next season.
"I hope this season is a good sign regarding the future. Our work on the field has spoken for us. We can do big things."