Rachel McAdams recalls being told she was ‘too old’ for the lead role in ‘Mean Girls’

Rachel McAdams made pop culture history with bitter teen queen Regina George, but her first audition for Mean Girls in 2004 was for a completely different role.

McAdams, an Ontario native, was originally cast as a stand-in for Cady Heron, the naive protagonist eventually played by then-17-year-old Lindsay Lohan. At age 25, “I remember thinking, ‘This is a useless exercise. I’ll never get hired to caddy,'” McAdams told PEOPLE on the stand in this week’s issue.

“I was just starting out and that was the main character,” the Send Help star continues. “I never thought I would be at a point in my life where I would be chosen for a role like that. So I just went in and had fun.”

McAdams, 47, recalls that he just wanted to be in a “great” Tina Fey movie. “I loved the script so much that I remember closing it, calling my manager, and saying, ‘I want you to play the role, even if it’s just one line.'”

Mean Girls director Mark Waters has added the ultimate twist. “You’re too old to play Caddy, but you’re perfect for Regina,” he said. “Regina has been around the neighborhood a few times and maybe she’s an old soul. I don’t know if I’d call her an old soul, but she’s got a lot more miles than Cady,” McAdams tells PEOPLE. “So I took that as a compliment.”

Then, in April 2004, “Mean Girls” hit theaters and history was made. “I love playing the villain,” she says. Two months later, The Notebook was released in theaters, establishing McAdams as a red-hot star on the rise.

The timing was “completely out of my control,” she says. “I once heard that if you’re lucky you might get your foot in the door, but you can’t stay in the room. I don’t know who said that, but I think it’s really true.”

She added, “These are two completely different movies in a row and both got some attention. So I think I was really lucky in that draw in my life.”

More than 20 years later, McAdams’ career has transcended genres and produced countless hits, from the iconic comedy Wedding Crashers (which she says was “so much fun” that the movie “didn’t feel like work”) and the best-selling film adaptation of The Time Traveler’s Wife to the blockbuster Marvel movie Doctor Strange and her Oscar-nominated 2015 Spotlight. “I feel really lucky to still be here,” she says. “I’m still pinching myself.”

McAdams’ new psychological thriller Send Help is currently in theaters.