You can hopefully get the exam deferred. You'll have to fill out this form:
http://www.ucalgary.ca/registrar/fil...F%20EXAM_0.pdf
The form makes it sound like it is very difficult to get an exam deferred but when I missed an exam I managed to get it deferred and my only reason was that I thought the exam was at 3:30 when it was actually at 12. When I was talking to the guy at the registrar he said that if you haven't deferred an exam in the past they will likely let you defer one. I hope it all works out for you.