The 2009 world champion has scored just two points from the first two races of the 19-round season and is 38 adrift of Red Bull's Sebastian Vettel.
Mexican team mate Sergio Perez has scored the same number of points.
Button told reporters at the Chinese Grand Prix that he was confident the team still had everything to fight for despite the setback.
"It was so easy for people after Melbourne to say we should go (back) to last year's car," he said. "It's really difficult to not think like that because in the last few races of the year we were quickest.
"But what we have done with the car I think is the right thing.
"It has hurt us a lot, especially at the first race, and it might still here and in Bahrain, but the idea was always to have a car that we could develop through the season and we felt that at the end of last year we were at the end of everything with last year's car."
The regulations are largely the same as last year's and McLaren had a choice between a simple evolution for 2013 or a complete redesign.
Unlike others, they opted for the latter course of action.
"I think the one thing that surprised us is that nobody else has gone our route," said Button. "We are the only team to do that. We expected all of the top teams to do the same thing so we didn't think we would have lost anything at the first race.
"We thought that the smaller teams would probably keep the same tub (chassis), go the same direction and just slightly improve through the winter and they would be competitive at first."
Button said that if McLaren could turn it around and be challenging at the front in the next few races then it would augur very well for the rest of the season because of the potential to be unlocked in their car compared to others.
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