The San Francisco Ethics Commission fined former Supervisor John Avalos $12,146 on Friday for failing to properly disclose campaign finances from his unsuccessful run for mayor in 2011.

According to the Ethics Commission, Avalos’ campaign committee improperly reported $26,506 — or 11 percent — of his total contributions. The committee also failed to maintain complete records for $391,594 worth of expenditures, 60 percent of the total amount of money spent.

Avalos accepted the settlement in front of the commission Friday. He blamed the oversight on inexperienced volunteers who were in charge of his finances.

“It was a grassroots campaign. ... We had very few paid staff,” he said in an interview. “I thought we were doing a fine job.”

During his 2011 run against late Mayor Ed Lee, Avalos — who served as District 11 supervisor from 2009 to 2017 — raised a total of $232,605 and received $461,479 in public financing, according to the commission. He returned $46,966 in unused funds to the city.

The commission did not realize the proper records were missing from the committee until it conducted an audit four years after the election.

“The consequences have gone on for a number of years, especially the work we did with the commission to recover the paperwork,” he said. “This has put a tremendous amount of toil on my life, and I’m eager to put it behind me ... starting tomorrow.”

Avalos said he would be more careful with his finances if he were to run for office again — a possibility he did not rule out. He will pay the fine with personal funds.

— Trisha Thadani

Email: cityinsider@sfchronicle.com, tthadani@sfchronicle.com Twitter: @sfcityinsider, @TrishaThadani