Robyn Jackson, 30, from Leeds, was catching some waves on her last trip before lockdown when a giant swell threw her off her board.
The finn then wedged through her wetsuit and deep into her leg - leaving her terrified and in agony.
But her injuries were compounded when the board broke free and smacked her in the face.
RNLI lifeguards at Harlyn Bay, Cornwall, hauled Robyn to safety before she was taken to the hospital for surgery on her leg.
She is now continuing her recovery at home and has posted pictures of her injuries on Facebook.
Alongside the images, she wrote: "What an absolutely crazy few days.
"What was supposed to be the last surf trip before lockdown and the weather gets worse.
"A surprise gift to collect a new surfboard resulted in a traumatic experience.
"A wave threw me off my board, wedging my surfboard finn through my wetsuit and deep in my leg.
"The wave then unweged it smacking me in the face.
"Daze and shocked, I was carried out of the water and ended up in A&E then being operated on.
"Safe to say I'm feeling worse for wear and will be hanging the surfboard for a while.
"The tag is all that is left of my wetsuit after being cut off me.
"They call it trauma for a reason."
The "dazed and shocked" surfer was carried out of the water by a family of lifeguards, Jason Dean and his sons Jordan and Jake on Saturday.
Robyn, who was left with a black eye, said the swift action of the lifeguards meant her leg wound was clean and the operation at the Royal Cornwall Hospital was a success.
She added: "They acted quick, got me out of the water and off the beach as I couldn't walk on my leg.
"I think I made their day a little bit more dramatic and exciting, but they saved me and my leg."
Max Setti, RNLI lead lifeguard supervisor, described it as a "a really major injury".
He added: "We're so pleased she is making a recovery.
"Thankfully she was at a lifeguarded beach and the lifeguards who are trained in casualty care to the standard of a first responder knew exactly what to do to treat Robyn quickly.
"It's great that she felt looked after and I am extremely proud of the team.