If you don't think you would be able to keep your words, then don't make any decisions.
I'm a pretty flexible person myself and I'm generally okay with everything ranging from direct discontent from people to cleaning a hellish kitchen but here's the catch: just don't mess with anything related to PROMISE.
I take any promises seriously.
Although I admit myself was not always right on the clock, I will still be there even though it means I'll be late. There's a reason why I rarely promise anybody about something because I don't know what will happen in the next few days.
Switching the topic to cancellation, even any major brand store's customer service will ask you to enquire and fill in the application form and wait for maximum 3 working days. NOT THE DAY WHERE YOU DECIDE YOU WANT TO CANCEL IT.
***it's actually even rarer for me to explode, or at least express anything here but I just need some place to throw this things up to let me concentrate on my exam tomorrow. Cheers.