In conversation with Today‘s Jenna Bush Hager at Hoover’s Book Bananza festival in Texas, the author shared details about the adaptation, saying that the choices fans have been concerned about were her decision.

One thing fans seem unhappy with is Lively and Baldoni’s casting, because in the book Lily is 23 and Ryle is 30, while Lively is 35 and Baldoni is 39. Hoover explained that she wanted to age the characters up in the movie in an effort to correct a mistake she made in the book.

Hoover continued, “There’s not a 20-something neurosurgeon. As I started making this movie, I’m like, ‘We need to age them out, because I messed up.’ So, that’s my fault.”

She pointed out that despite some of the backlash, she’s “extremely happy” with their casting, sharing that she’s been “obsessed” with Lively since Gossip Girl and couldn’t believe that the actress had agreed to star in the adaptation.

“I was like, ‘Yeah, OK, that’d be great,’” she said. “I think [Baldoni, who is also directing and executive producing,] expected [me] to just scream into the phone. But he doesn’t realize … I have not allowed myself to get truly excited because I’m like, something could happen. It’s not done filming. Anything could go wrong.”

The author also addressed the conversations surrounding Lily’s outfits, which had been photographed in New Jersey before production shut down due to the writers strike.

She said she didn’t really imagine certain outfits when she was writing the book but “loves” the conversation that the photos have generated because it means that people care.

Lily’s style has been described as disheveled and hard to predict, as she wears camouflage some days, blue boxers under patterned pants other days and sometimes multi-colored baggy sweaters.

According to its description, It Ends With Us follows Lily after she moves to a new city, where she meets and falls for Ryle, a neurosurgeon, whom she has an abusive relationship with. Then, her first love, Atlas (Brandon Skelnar), reappears and challenges the new relationship.

Despite the concerns fans have, the writer believes that when It Ends With Us comes to life on the big screen, the movie people want is the movie they’re going to get. She shared that she saw some footage when she visited the set, and she cried “so much,” even though she insists she’s not an emotional person.

“You guys are going to be so happy,” Hoover said. “I’m extremely happy, and now my expectations are up, and I’m going to keep them there.”