She said she was a "perfectionist" and wanted her performance for President Barack Obama to be a memorable one. She called the day "emotional".
Beyonce opened the press conference with a live rendition of the national anthem.
"I practise until my feet bleed and I did not have time to rehearse with the orchestra," she said. "Due to no proper sound check, I did not feel comfortable taking a risk.
"It was about the president and the inauguration, and I wanted to make him and my country proud, so I decided to sing along with my pre-recorded track, which is very common in the music industry. And I'm very proud of my performance."
She asked those at the conference to stand before she belted out The Star Spangled Banner, and after she said with a laugh: "Any questions?"
The star had not spoken publicly since it was alleged that she lip-synched her rendition of The Star Spangled Banner at Mr Obama's inauguration
Her critically praised performance came under scrutiny less than a day later when a representative from the US Marine Band said she was not singing live and the band's accompanying performance was taped.
Shortly after, the group backed off its initial statement and said no one could tell if she was singing live or not.
The half-time performance became a main focus of her afternoon press conference, even though she would likely rather concentrate on questions about her set list for Sunday and her upcoming HBO documentary, Life Is But A Dream.