The "All About That Bass" singer, 21, is recording a new song for The Peanuts Movie, titled "Better When I'm Dancin' ", that's all about letting go of your insecurities and embracing your true self on the dance floor. Trainor spoke to PEOPLE about what it feels like to officially join the Peanuts gang.
What inspired the film's song?
They wanted a song about confidence and knew I was good at writing those. I feel better when I'm onstage dancing and having fun, so I wrote about that!
What did you think of the animated version of yourself?
Isn't it so cute? They sent me the first version and I said, "Don't touch it, it's perfect." It's the background on my phone!
Were you a big Peanuts fan growing up?
My grandma always had it on; she always had a lot of cartoons on. I was super-duper young, but I do remember when the show was on – it was huge!
I like Charlie's sister [Sally Brown]. She's a cutie. I also like the new girl – no one knows about [her] yet, but I do! I can't wait for everyone to meet her.
Which character would you be friends with?
Charlie, because I felt so bad for him in some parts. I'm probably the person that would go make sure he's all right. We would be best friends.
The Peanuts Movie hits theaters Nov. 6, 2015.