"I am a perfectionist," People.com quoted her as saying at a Super Bowl news conference in New Orleans.
She opened the news conference by asking reporters to stand and then singing "The Star Spangled Banner" a cappella -- drawing cheers and applause.
"Any questions?" she said.
"One thing about me, I practice until my feet bleed. I did not have time to rehearse with the orchestra. It was a live television show. It was a very important emotional show for me, one of my proudest moments," she said of her performance at the inauguration.
"Due to the weather, due to the delay, due to no proper sound check, I did not feel comfortable taking a risk. It was about the president, the inauguration. I wanted to make him and my country proud, so I decided to sing along to my prerecorded track, which is very common in the music industry. I'm very proud of my performance."
Beyonce is to sing at Sunday's Super Bowl halftime show.
"I will absolutely be singing live," she said at the press conference. "This is what I was born to do."