"I have never performed with another person before so this brought out a whole new side of me," she said.
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Mach is a sophomore at New Paltz High School who turned 16 on Monday.
Laila Mach says before 'American Idol' she never did this
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As one of the youngest contestants this year, she performed "Fix It To Break It" by Clinton Kane during the Genre challenge to advance.
"Some people sound 15, and then some people don't sound 15," Katy Perry said after the performance.
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Mach chose that song because she said got her through a break-up last year that caused her to stop playing music for a while.
"I realized that no boy is worth putting my music to the side," she said.
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Mach said being on 'American Idol' has taught her a lot about confidence.
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"I was always worried about how the other people were going to hear me and I was worried about pleasing the audience. I think what's more important is to please yourself and have you be proud because if you are proud of your own performance, it doesn't matter what anyone says to you," Mach explained.
UPDATE: Laila advanced to the next round with her Duets performance.
You can see every performance on American Idol's YouTube channel and watch the full episodes anytime on Hulu.