The Briton, who won the world championship in 2009, finished ninth in the opening race of the season in Melbourne.
"It's not a great result, but us we did everything we could," BBC Sport quotes him as saying.
"We should be happy with our job today but not happy with the pace of car. We all need to pull our heads together to find a way forward.
"We've still got to aim for the world championship. It's going to be very difficult for us considering where we are but it has to be the aim when you are driving for McLaren. It's just going to be harder than what we thought."