"When I did this now I said, I probably, maybe will confuse people," Trump told NBC News.
Trump said he wanted the FBI's investigation into Russia's election meddling to be "absolutely done properly."
Earlier Thursday, White House deputy press secretary Sarah Huckabee Sanders said the Comey firing may hasten the agency's investigation into Russian meddling.
"We want this to come to its conclusion, we want it to come to its conclusion with integrity," she said, referring to the FBI's probe into Moscow's interference in last year's election. "And we think that we've actually, by removing Director Comey, taken steps to make that happen."
The statement had come as a surprising admission from the White House that Comey's sudden dismissal on Tuesday may have an effect on the Russia probe. Officials have insisted the removal came because of Comey's handling of an investigation into Hillary Clinton's email server, and was unrelated to his oversight of the look into Russia's election hacking and possible ties between Trump advisers and Russian operatives.
Earlier in her briefing Thursday, Sanders claimed that Comey's firing had not altered the Russia investigation at all.
"Any investigation that was taking place Monday was taking place today," Sanders said, suggesting that was an indication that Comey's firing would not impact the ongoing probe.
Sanders said Thursday that Trump would "love nothing more for this investigation to continue to its completion."
Trump himself has cast doubt on the investigation, suggesting any question of ties between his campaign and Russia are a "hoax."
Trump said Thursday he wants to get to the bottom of Russia's meddling in the US presidential election.
He insisted that his firing of Comey would not put a damper on the FBI's probe into the matter.
"I think that we have to get back to work but I want to find out -- I want to get to the bottom. If Russia hacked, if Russia did anything having to do with our election I want to know about it," Trump said.
"If Russia or anybody else is trying to interfere with our elections I think it's a horrible thing and I want to get to the bottom of it and I want to make sure it will never ever happen," Trump said.