Hi Ahmed,
First do not panic. You have 15 days to go. So I would recommend doing the following:
1 take another mock exam.
2 review the areas that you are weak in.
3 spend one week studying those areas
4 take a further mock exam
5 did you improve? Yes then carry on studying weak areas and taking mock exams every 4 days until your exam.
6 If no, then consider delaying your exam until you are ready - if you are close to the time limit then you may want to take, but if you are not close to your time limit then take the time to get ready.
This is a hard exam, so you need to ensure that you are getting 80% on the mock exams to feel confident going in.
Good luck and let us know how you get on.