An acceptance into a program is contingent upon successfully completing any outstanding prerequisites. And as far as I know, you have to get a C or higher in any outstanding prerequisites. So, yes, your acceptance can be denied if you don't hold up your end of the "deal".
Keep working hard. I know how frustrating it is to have a bad department at a university. I would go talk to the professor and tell him/her your situation. Go to extra office hours. Do whatever you can to make him/her see that you're trying your best. Find a way to get a C or higher. I know you can do it 🙂
* or, as mrleroy said, you may even have to get a B or higher. Regardless, do whatever is in your power to raise that grade! *