Quite a few people I went to uni with picked up a fail sometime through their time at Uni.. I wouldn't stress about it too much. You can always take it again.. or do another class (if you don't want to do macro again
). Most uni's even have a summer school program so you can pick up that extra credit (besides taking on an extra unit during the year).
Still, if you have the opportunity to sit the Supp.. do what you can.. put in the hard yards for the next day or two.. and hopefully you'll scratch by w/ a 50
Edit:
Also, if macro is a core subject for your course, I'd definitely try to pass this supp exam.. as cores are usually cores for a reason.. and you may end up not being able to get into other classes because that one's required. I don't know if this is the case, as I was a comp nerd, not a Commerce student hehe.