Assuming you are doing higher level?
It depends. What type of student are you?
i) Are you the type who wants to cover the whole course, regardless? If you are then Yes, you will need to learn everything.
ii) Are you willing to study intelligently? If you are then choose your topics carefully (check past papers), and you will be fine - in other words No.
Recommend you check www.precisionrevison.com especially if you fall into the second group.