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When Rebekah Gregory was 10 years old, she made a promise to herself that she’d write a book by the age of 30. Little did she know what a story she’d have to tell.

Gregory, 29, survived the Boston Marathon bombing of 2013 along with her son Noah, now 8, and then-boyfriend Pete DiMartino. The three were at the finish line, waiting for DiMartino’s mom to cross, when the explosions happened. Months of physical therapy – not to mention emotional healing – followed for all three, and Gregory was ultimately fitted with a prosthetic leg. Since, she’s weathered a dream wedding to and subsequent split from DiMartino, remarriage and the premature birth of her daughter Ryleigh, now 2 months.

“As a little girl I had no idea that my crazy life would give me so much material to fill the chapters with,” Gregory tells PEOPLE exclusively. “But now here I am, and the neatest part of all is that my book is set to be released on April 4, 2017 – eight days before my 30th birthday.”

Calling the writing process “one of the hardest things I have ever done,” Gregory promises that the pages will go beyond what happened in Boston. “Each chapter was like a form of closure to the real-life ones that I had never really healed from, a lot of which are completely unrelated to what happened in Boston and the recovery after. There are parts to my life that even my closets friends don’t know.”

But what she does know is the goal of her story: to give others hope. “If I’ve learned one lesson, it’s that each of the hardest chapters in your life brings you to the most beautiful ones of all,” she says. “You just have to keep going long enough to get there.”

Doing “wonderful” since her recent marriage and birth (Ryleigh is now healthy and home with the family), Gregory, who ran the Boston Marathon in 2015, admits she still has PTSD and ongoing difficulties with her injured leg.

“There’s nothing I wouldn’t give to go back to life before I ever went to the Boston Marathon, but I can’t,” she shares. “What I can do is appreciate every new moment I’m given. I’ve been given a huge platform – along with the other survivors – to potentially help other people through what we’ve been through. If I have that ability when I wake up every day, what more could I ask for? I just want to be a mom that one day my kids will be proud of.”