You'd be surprised how many similarities there are between training for a marathon and working on a writing project. Both are about showing up and doing the work.
Write your book one scene at a time. Learning how to write a scenes is key if you want to be a professional writer.
Writing memoir or creative nonfiction requires you to be vulnerable and honest. How comfortable are you putting yourself on the page? Essayist, novelist, and CNF writer Jo Ann Beard is a master of flexing the vulnerability of humans.