structured approach

so i have perfectionistic tendencies.whenever i want to achieve any goal i need to plan it, want it structured, i go into detail about where , when , how it should be done. example- i plan to finish a book in exactly 15 days , i will consider how many pages should i read per day, where , at what time etc. the thing is that when i am unable to finish it in my given time or it deviates from my perfect plan i want to give it up and start all over and it create distress in me. so how do i overcome it? how do i become more flexible? should i do things randomly without planning? should i as a perfectionist follow structured approach? is structured planned approach towards more efficient than doing things randomly?