The 26-year-old star has resisted offers to present the iconic comedy show for years and now she's finally decided to "bite the bullet", Kristen admits to suffering some last-minute nerves.
She shared: "For six years I've been a total wuss about it, and then I was finally like, at some point you have to bite the bullet, you know ... and just fail.
"It makes you stronger, man!"
Kristen revealed she felt similarly nervous during the making of her new movie 'Personal Shopper', for which she rode a scooter in France without any meaningful training.
She told 'The Tonight Show Starring Jimmy Fallon': "They kind of let you do anything.
"Like I rode a scooter in the movie, I had two hours training beforehand. I feel like in the States they'd probably have me for a month with certification, insurance and all this stuff ... I was genuinely terrified."
Meanwhile, Kristen recently admitted to making a "million bad movies" during her career.
The actress and director - who has starred in the likes of 'Twilight', 'Equals' and 'Snow White and the Huntsman' - said it is "rare" that something turns out exactly as she had hoped.
Asked how she would describe herself as a director, she said: "I'm a pretty obsessive person, which is I think entirely necessary. You have to be a little crazy to put yourself through something like that and actually make it happen.
"I was probably a little bit more controlling than I thought I would have been. My favourite thing in the world is when it feels like something starts to get up and walk itself.
"When something's really good, and it's rare - honestly I've made a million bad movies. Not bad, it's just like sometimes they don't come together in a way that feels miraculous and when they do, it genuinely feels like something is floating and you're all sort of blowing on it to keep it up and it's like, that fully happened.
"It's so cliché, it feels like super pretentious to say this, but you genuinely feel like this vessel and you're like, 'That was sick, I don't even know what just happened,' and it's just f***ing real."