06/14/2012 AT 06:25 PM EDT
When Olympic gold medalist Shawn Johnson took a break from gymnastics – and her six-day-a-week workout routine – after competing in the 2008 Olympics
, she experienced a weight gain of 25 lbs.
"I was just going through so many different life changes," Johnson, 20, tells PEOPLE just 11 days after announcing her retirement
from competitive gymnastics because of a 2010 knee injury.
"I was traveling so much, I didn't get the opportunity to work out. I thought I could do and eat whatever I wanted because I was fit."
This time, she says she's going to be more careful.
"I'm sure it's not going to happen again," she says. "I'm going to try to work really hard and make sure of that. I feel like I'm mentally in a different place so I know how it all works."
Since her June 3 announcement, Johnson has had plenty of offers
come her way – from commentating gigs to appearances. But she's taking her time sifting through them.
Other than attending the Olympics in London next month – courtesy of a few of her sponsors – and a short book tour for her recently released memoir, Winning Balance
, she has no firm plans.
"I'm trying to relax a little bit," she says with a laugh. "It's the first days of relaxation I've had in a few years."
She also says it's a relief to have the decision not to compete safely in her past. After two surgeries and four cortisone shots on her left knee, which she injured skiing, doctors told her she risked damaging it permanently if she continued with gymnastics.
"I'm happy, on my way to getting healthy again," she says. "Having that stress off me is definitely liberating."