AceShowbiz - "Fight Song" singer Rachel Platten has apologised for messing up the U.S. National Anthem at a women's soccer game on Saturday, April 14. The pop star restarted "The Star-Spangled Banner" twice before the match in Utah after realising she'd forgotten the opening line of the Francis Scott Key song. She then asked for help with the lyrics, stating, "I'm so sorry... Could someone tell me the next line?"

Now she's speaking out about the blunder, confessing she still feels "really embarrassed."

"I'm having a hard time forgiving myself, but I'm working on it," she tells People. "It was incredibly, incredibly embarrassing... I've been trying to retrace steps of what happened... It has just been hanging over me."

"I was so nervous going into it. The anthem is such a big deal; it's probably the most important song for our country. I always get nervous because it means so much because it is so powerful. I always want to do it justice, do a good job and give people the exact version they expect and they want."

It wasn't the first time Platten had tackled the song at a sporting event, but for some reason her mind "just went blank" as she started to sing.

"I stepped in front of the people and I felt the expectation," she adds. "I was ready to open up and do it, and my mind just went blank... It was like a test that you know all the material to, you study so much and you get in there, and your mind doesn't co-operate."

"I was proud that I was able to finish... I actually can't believe I didn't forget more words and that I was able to complete the song... (I thought), 'I really want to run out of the stadium right now, but I'm not going to do that. I'm going to finish this song.' "