Outgoing Health and Human Services (HHS) Secretary Kathleen SebeliusKathleen SebeliusLeaked email: Podesta pushed Tom Steyer for Obama’s Cabinet Romney: Trump victory 'very possible' Fighting for assisted living facilities MORE said she was "flat-out wrong" to believe that HealthCare.gov was ready to go on Oct. 1, 2013.
In candid remarks about the healthcare rollout, Sebelius said she regretted not taking a different approach when HealthCare.gov was under construction.
"If I had a magic wand and could go back to mid-September and ask different questions based on what I know now," I would, she said. "I thought I was getting the best information from the best experts but clearly that didn't go well."
"The launch of the website was terribly flawed, terribly difficult," she added. "Could we have used more time and testing? You bet."
The former Kansas governor handed in her resignation to President Obama in early March, when the enrollment numbers on the exchanges began to rise.
She said she knew around the time of the election that she would not stay through the second term, though she starting discussing her departure with Obama after Jan. 1.
"I made a decision at the election that I couldn't leave with a lot of my [Cabinet] colleagues," she said. "That did not even seem like a topic to consider."
Asked whether she was pushed out of the administration, Sebelius insisted the departure was her choice.
"I thought that at the end of open enrollment was a logical time to leave," though there is "never a good time," Sebelius said.
"I made it pretty clear that it really wasn't an option to stay on," she added.
As the official in charge of the healthcare rollout, Sebelius was blamed for the massive technical problems with the federal enrollment website, and soon became the target of partisan attacks over the law itself.
She said Sunday that while the exchanges were a "moving target" — states were still deciding in early 2013 whether to run their own systems — "clearly, the estimate that it was ready to go Oct. 1 was flat-out wrong."
"That was very alarming" when HealthCare.gov crashed for the first time, she said, "because that took some real diagnostics in terms of what the problems where and then analysis" about whether the system could be fixed.
"The good news was that we said it would be fixed in eight weeks, it was fixed in eight weeks and we announced last week that 7 million people ... had enrolled," she said.
Sebelius did not mince words when describing the pressure of last fall, calling October and November a "dismal time."
It was a "pretty scary thing" preparing for Dec. 1, the administration's publicly announced deadline for making the site work, she said.
"It was awful. It was awful. But all you could do is say, 'We're going to fix it' [and] 'Hold me accountable.' "
Obama has nominated White House budget director Sylvia Mathews Burwell to replace Sebelius at the HHS. She is expected to be confirmed when Congress returns from its April recess.
—This report was updated at 11:24 a.m.