“I’m perfectly comfortable signing the bill,” he said. “I’m only acknowledging that it became a big distraction even though everything was done properly.”

Mr. de Blasio’s 2013 campaign took the same approach in responding to the finance board, which found that his campaign had made late filings, accepted donations over the city’s strict limits, and spent money that could not be documented as related to the campaign.

A detailed breakdown by the board of the improper spending included $550 on makeup for television appearances by Mr. de Blasio and his family on election night; $298 on a flight to Washington for his son, Dante, to attend a 2010 rally hosted by the Rev. Al Sharpton; and more than $116,000 in postelection payments to Hilltop Public Solutions, a public relations firm, that were not fully explained as campaign related. (Bill Hyers, a partner at Hilltop, ran Mr. de Blasio’s campaign and helped start the Campaign for One New York.)

According to the board’s report, the campaign said the presence of Mr. de Blasio’s son at the rally commemorating the anniversary of Martin Luther King Jr.’s “I Have a Dream” speech, was appropriately paid for with campaign funds because his son, who is black, appeared at the event as “a visible manifestation of how the candidate’s life experience was resonant to the spirit of the occasion.”

Dan Levitan, a spokesman for the campaign, defended the spending on makeup and said the travel to Washington “was an important trip taken as part of the campaign,” even if the mayor had not at that point formally declared his candidacy. Mr. Levitan said the fines would be paid out of money raised in anticipation of a 2013 runoff.