Compulsory pre-sessional course, Mathemathics

Hi

I am accepted to Msc Economics and Management, and have to take a compulsary mathemathical course that starts the 9th of September. It has a mathemathical part which I am worried about as my mathematics are quite weak. In high-school (A-levels) I dodged mathematic modules whenever possible which lead to my failure of grasping mathematical principles and rules which should work as a foundation to build upon. I survived nicely throughout uni by learning the necessary rules for each exam, however if something unexpected appears I am in trouble. So how difficult and this pre-sessional course and should I start early to revise? I am busy working this summer, but putting in hours shouldn't be difficult.

Thanks for help!