The company's CEO Zuckerberg will be meeting U.S. lawmakers on Tuesday and Wednesday to present his case.
"We didn't take a broad enough view of our responsibility and that was a big mistake", Xinhua quoted Zuckerburg as saying in a prepared testimony released by the US House Energy and Commerce Committee.
Zuckerberg will also testify about how Russian Federation used Facebook to influence the outcome of the 2016 presidential election.
In it, Zuckerberg says Facebook is "an idealistic and optimistic company" that focused on the good that can come from connecting people, such as organizers of the #MeToo movement and the student-led marches against gun violence.
About 310,000 Australian Facebook users are set to find out their personal information may have been accessed by Cambridge Analytica.
Sen. Bill Nelson, D-Fla., said Zuckerberg told him during their one-on-one meeting that the company had been "lied to" by Cambridge Analytica when officials there told Facebook that they had gotten rid of all the user data they had collected through a research app, after the company banned those data collection methods.
"Using as expansive a methodology as possible, this is our best estimate of the maximum number of unique accounts that directly installed the thisisyourdigitallife app as well as those whose data may have been shared with the app by their friends", the company said.
A spokesperson for Facebook did not immediately respond to a request for comment.
Facebook "happens to be the point of the spear, but all these other app sites that get your personal data, that's another way of us losing our privacy", Nelson said.
It comes after Cambridge Analytica developed controversial tools for use in political campaigns and worked on Donald Trump's run for USA president.
The next two days will be important to the growing concern of privacy on an uncontrolled social media. Facebook is also under investigation by the Federal Trade Commission, which is evaluating the company's compliance with a consent decree, finalized in 2012, which settled FTC claims that Facebook's privacy practices were deceptive.
Facebook has admitted the personal information of up to 87 million users may have been improperly shared with political consultancy Cambridge Analytica.
He will also likely face questions about ads and posts placed by Russian operatives, in what USA authorities believe was an attempt to influence the U.S. 2016 election. Advertisers will first have to be approved by the social media company, although that vetting process remains unclear.
But Facebook critics counter that "responsibility is not transparency" and that the real issue is the hubris that pervades Silicon Valley, where regulation is often overridden by shareholder profits. Though it only takes one Facebook user to expose their friends' data, users have since been encouraged to change their privacy and advertisement settings.
On Capitol Hill, U.S. lawmakers signaled they want action, not just contrition, from social media executives.
It's the first time Zuckerberg will personally sit for questions from Congress, instead of sending a deputy. "We've gone for many years in the United States believing that self-regulation could work - that Facebook and the other tech giants could police themselves, but I think very few people still believe that".
In the testimony, Zuckerberg acknowledges that the questioning will likely be critical.
"The bottom line here is: if Facebook cant fix its privacy problems, then how can Americans trust them to be caretakers of their sensitive information?" he asked.