"[I went with] a group of friends," the actress told PEOPLE while hosting the UCLA 5K Run/Walk on May 23 benefiting the Child Life/Child Development program at Mattel Children's Hospital. "I think you put more effort into getting ready before than actually you spend at the place. But it was so much fun."
Fanning, 16, currently a junior and a varsity cheerleader at an L.A. high school, says she's "lucky" to be able to have a movie career while going to school – where she isn't treated differently because of her Hollywood status.
"I've been able to have a really great experience and it's almost over. I can't believe it!" she says.
Outside of school, Fanning's enjoyed another kind of experience: Being part of the Twilight worldwide phenomenon as the villainous Volturi Jane.
"It's so fun," says Fanning about filming with the cast in Vancouver. "I've done a few movies with Kristen Stewart now, and she's become one of my best friends, so it's always fun to be with her. The cast is also fun and so nice and [we] have really become very close."
Working with Stewart on another film, The Runaways, in which the two stars shared a kiss, also brought them close, says Fanning.
"We have a really close bond in the film so it allowed us to have a really close bond in real life as well," she says.
As for whether she's Team Edward or Team Jacob, Fanning is playing it neutral and staying tight-lipped.
"I will get in trouble if I [picked] one," she says.
Reporting by BETHANY POWERS