Carrie Underwood‘s cover of Heart’s “Alone” on American Idol is now one of the most memorable performances from her winning run on the show back in 2005.

But at the time she sang it, Underwood admits she was nervous. In fact, she thought for sure that the judges and the audience alike were going to “hate” her version.

The singer remembered her Top 11 “Alone” performance in a new social media video, filmed as part of her current run as a judge on Idol. In the clip, she explains that she chose to do this song during a week when all contestants had to sing No. 1 hits, from an array of different years.

“I feel like this one that was kinda in my back pocket from the beginning, even before I knew what the themes were gonna be,” Underwood remembers.

She knew she could hit the high notes, and as a country singer, she wanted to show her rock ‘n’ roll side. She also knew that the judges had been critiquing her for “playing it so safe” on the show.

But still, taking the risk was nerve-wracking.

“I think I even remember, like, writing in my journal how much they were not gonna like me singing this song. ‘They’re gonna hate it. Whatever. I really wanna do it, so let’s go. You never know what’s gonna happen,'” she remembers thinking.

Almost as iconic as her performance itself is the teased-to-Jesus big hair that Underwood was rocking when she sang “Alone.” Her look for this episode made her a little nervous too, she says.

“That was some big hair,” she comments now, acknowledging that, of course, the stylists were drawing inspiration from the fashions contemporary to this 1987 hit.

“But I was kind of self-conscious of it in the moment,” Underwood continues. “It was a little … not how I was used to seeing myself.”

“Of course now, it’s iconic. Wouldn’t change a thing. But at the time I was nervous,” she adds. “I hadn’t fully embraced the fact that I was playing a character, getting into a role. Now I’ll do that at the drop of a hat. “

Read More: Remember When Carrie Underwood Covered Heart’s ‘Alone’ on American Idol?

But after Underwood concluded her performance — to rousing praise from all three judges — she was nervous for a whole different reason: Simon Cowell made a bold prediction about her career that she thought might make her unpopular with the rest of the contestants.

“I will make a prediction,” Cowell told her as he reacted to her song. “Not only will you win this show, you will sell more records than any other previous Idol winner.”

“What an incredible prediction,” Underwood says, looking back. “On one hand, I think at the time I thought this was amazing. And then I thought, ‘I have a target on my back now. Everybody’s gonna hate me.'”

Cowell’s prediction would go on to be correct. Not only did Underwood win her season of Idol, but she has gone on to sell more than 85 million records worldwide to date, beating out Kelly Clarkson, who is the second-best-selling Idol winner at 82 million records sold.

Ultimately, Underwood says that her banner performance was worth feeling like other contestants might dislike her.

“The compliment outweighed the fear,” she says, “because that was just incredible. I know I slept well that night.”