Welcome to MacInsiders! Congrats on choosing Mac as your first choice, a great choice!
As Starfish said, the way the cut off works is not guaranteed, but more of an estimate.
None of the items you mentioned (summer vs regular courses, private school, etc) affect your chances, in the end it's your grade average that gets you ranked on the admissions list, and then they send out offer letters to x number of people to reach their goal amount of students they aim to have for the year.
At this point just continue to wait for an offer.
Last year the admission average I see listed is 89% which is on the higher end of that range you mentioned. http://future.mcmaster.ca/2015/05/13...sion-averages/
But keep in mind that the standard decision deadline is near end of May, so they still have weeks to send out more offers. You might still get one
Best of luck.