McLaren boss Whitmarsh said last week that he felt Hamilton had some doubts about his move given his team's and Mercedes's current form.
"Probably, when you make a decision you have to tell yourself that the decision is made so you have to look forward," Whitmarsh told the official Formula 1 website when asked if Hamilton has regretted his decision.
"He's not going to say 'hey, they offered me more money'. He's also not going to say that he's made an awful mistake. I hope he thinks today that he's made an awful mistake and I hope he thinks that next year.
"He's made that decision and he has to live with that decision."
Hamilton, who has been with McLaren since he made his F1 debut in 2007, said ahead of the United States Grand Prix that he was surprised by Whitmarsh's comments.
"I was a little bit surprised to hear that because it's definitely not the case," said Hamilton on Thursday. "But I've got a great team and I've been with them a long time.
"I'm sure everyone has emotions within the team, but I'm still here giving 100 per cent to them for the last two races. Of course it's quite emotional for me but I'm very, very happy with my decision."
Hamilton is already out of contention for the 2012 championship after a troubled second half of the season, but the Briton insisted he is still determined to fight for victory in his final races with McLaren.
"It is what it is. I'm happy just to be here fighting in the last two races for my team," he said.
"I just want to do the best job. We can still fight them, even though we are not fighting for the championship."