Great idea doing the subjects that you can in your own time. LOL, only because I did the same thing.
I did everything at home except for flight planning and no matter what I did I could not pass the exam.
Booked myself into Nathan Higgins in Marochydore and he found my problem on day 2 of the course. Makes me laugh that it was such an easy fix, and after that he just made me faster. This course is so effeceint that on the day of the exam I had time to do it twice, and I'm not the sharpest tool in the shed. Now I didnt get 100% but a score in the 90's was good enough.
Keep at it and when you finally get stuck call this guy. Never give up there is always a solution.