Following Schedule 100%

I am having a hard time staying committed to my scheduled 100% because for one reason or another I miss a scheduled event on my calendar and then when I note my accomplishments in the homework for that day I only complete 66-80% of my scheduled day. I have recently decided to just plan a day the way I usually do and now knowing that I miss at least 20% of my schedule, that I would decide AHEAD OF TIME to schedule free time for 20% of my tasks. How can I support myself enough to follow my schedule 100% of the time? Should I note how I might be over-scheduling myself and do this 20% tactic or should I challenge myself to follow 100% and just note the thoughts that are causing me to not be 100% committed?