p4 in 3 weeks?

This is a strange question. Nothing is impossible; the pass mark is 50, if you get lucky with the questions you could always pass. But without anyone saying anything you must already understand that this is not an ideal scenario and you are going to need to devote an awful lot of time to this over the next three weeks.

Having not passed P4 yet, I don’t feel qualified to give you advice on precisely what you need to do in order to achieve this but in general, as with all P level exams, there are no silver bullets; you will need to know the syllabus thoroughly and have done a fair few practice questions.