WASHINGTON (AP) — The Obama administration's timeline for having ready the new health care law's online sign-up system "was just flat out wrong," outgoing Health and Human Services Secretary Kathleen Sebelius said in an interview that aired Sunday.

The departing health chief also said the two months when healthcare.gov was plagued with technical problems were "a pretty dismal time" and the low point of her five-year tenure. But she defended the law's impact and said millions of Americans now have access to health care because of it.

"People have competitive choices and real information for the first time ever in this insurance market," said Sebelius, who last week announced her resignation.

But she acknowledged the rocky rollout for the online sign-up system fraught with technical problems that left Americans frustrated.

"Clearly, the estimate that it was ready to go Oct. 1 was just flat out wrong," Sebelius said.

HealthCare.gov was envisioned as the principal place for people to buy insurance under Obama's health care law. But its first few weeks were an embarrassment for the administration and its allies.

"Well, I think there's no question — and I've said this many times — that the launch of the website was terribly flawed and terribly difficult," Sebelius said.

Obama set a Dec. 1 deadline to have the website repaired, a move that left Sebelius nervous, she said.

"Having failed once at the front of October, the first of December became a critical juncture," she said. "That was a pretty scary date."

Sebelius' resignation comes just a week after sign-ups for insurance coverage ended, enrolling 7.1 million people and exceeding initial expectations. Enrollment has since increased to 7.5 million as people were given extra time to complete applications.

The departing secretary said she decided after the 2012 presidential election that she wanted to leave the administration but decided to stay through the sign-up period. Sebelius said Obama did not try to convince her to stay through the end of his term.

"I thought it was fair to either commit till January of 2017 or leave with enough time that he would get a strong, competent leader," Sebelius said.

Sebelius spoke to NBC's "Meet the Press."