The Northern Irish teenager impressed the Black Eyed Peas star on Saturday night to win one of the final spots on his team.
Sophie performed Estelle's American Boy on the show, and recalls: "I went out and just gave it my all and when no one was turning around I saw nervous."
Fortunately Will did press his buzzer, with moments to spare.
"I feel like I'm dreaming," says Sophie, who was hoping that idol Danny O'Donoghue would be the one to press his buzzer.
Sophie however insisted she wasn't disappointed.
"I think Will's going to help me so much because he knows his stuff," she explained.
The youngster added: "I just think he's going to help me be so cool because he's cool. I've taken such a huge step into what I want to do. When I hugged Will.i.am he was like 'You're dope' and W was like 'Waaaa'"