I’m in the same position as you. Passed every exam first time until I got to P4 and failed with 42.
It depends on where you went wrong. If you think it was knowledge, then you need to re-read your notes. I’ve always made mind maps of all my exams and read them on the morning of the exam which has got me through in the past. I’ve also worked through a lot of exam questions.
I think I failed in P4 because I simply wasn’t quick enough with the calculations. I knew what I was doing, but was just too slow and couldn’t get it all down on paper. My plan for the next 7 weeks is to practice each of the different calculations over and over again until it becomes automatic.