Seyfried said she took "the responsibility very seriously of portraying and giving her validation and being her voice," especially after meeting her children, "which is why I was so nervous about releasing it into the wild."
Still, she's delighted the film premiered at the annual independent-film showcase.
"I just am so, so happy and proud to be able to say that this is our premiere," she said. "It's here and it feels safe here almost for some reason, I don't know why. Maybe because it's just really cozy and everybody is really friendly."
But she acknowledged she's still frightened about how the film will be received when it reaches a wider audience. Earlier this week, it was acquired by the Weinstein Co.'s Radius label for North American distribution for a reported $3 million.
"It's scary. I'm really scared," Seyfried said. "I don't know what's going to happen after it comes out. But I would never take it back. I'm really happy that I was able to give her the voice that she never got to have."
AP Entertainment Writer Sandy Cohen is on Twitter: www.twitter.com/APSandy.