The singer told Grazia that she feared she was not famous enough for the panel of the reality talent show.
"I thought the BBC was making a mistake asking me to do it in the first place," Jessie J admitted.
"I kept saying, 'People might not know who I am!'."
She added of this weekend's final: "It's been an honour to be part of a TV show that celebrates the voice. It will be a massive night for the artists, coaches and crew."
Of claims that she has acted like a diva, Jessie J said: "There isn't anything flash in my dressing room. No champagne. No yoga mats or anything. That was meant to be one of my diva demands.
"I did ask for a scented candle. I don't think it's too much to ask for a nice, relaxing smell in the room. I also asked for a lava lamp."
She continued: "When I was a kid, they used to have a room at Great Ormond Street Hospital where you'd go and chill out. It was full of lava lamps and water lamps and since then it's always been a way to help me wind down. I never got one, and that's okay.
"But is there anything wrong with asking for what you know is good for you? Does that make you a diva, a pain? Or does it make you someone who knows what they want?"
