I had to cancel my gmat exam (weeks in advance to taking the test) as I simply did not think I would be ready come test day. Will this affect me applying in the future? In other words, would business schools be able to see that I cancelled my GMAT?
If you cancel your appointment, the schools will not see it. It is not the same as canceling your score or not showing up to the test.
No, it will not affect your chances later on and even if you reschedule (cheaper), they won't know either.