Livvy Dunne got the full acting experience before joining "Baywatch" ... revealing she first had a taste of rejection ... and it's all thanks to "The White Lotus!!"

The former LSU gymnast explained how she earned her red swimsuit on "The Tonight Show" on Wednesday ... admitting her foray into entertainment didn't go so swimmingly at the start.

She told Jimmy Fallon she did an in-person tryout for the hit HBO show ... and her nerves were off the charts. Ultimately, they elected to go with someone else for the role.

She said the audition was nothing like gymnastics ... 'cause while performing on a four-inch balance beam is a walk in the park, pretending to be someone else in a room full of strangers is not.

Dunne didn't give up, though ... and it certainly worked out in her favor -- as the footage from "Baywatch" so far looks great!!

Dunne was announced as the latest cast member for the highly anticipated reboot back in March ... and she'll be sharing the screen with beautiful ladies like Brooks Nader and Shay Mitchell.

Sounds good to us!!