As Teddy R says you must know your subject. I warn students time and time again it is not a remember the database exam, unlike Air Bore, HPL as it is so easy to change the parameters/numbers. Learning answers for GN practical questions is asking for a fail.
You MUST be able to use a CRP-5/Whiz-wheel with confidence, accuracy and speed, if you can't then you are wasting your time & money sitting the exam as you shall fail, due to lack of skills and then lack of time.
Convergency & departure does cause students problems for various reasons but there might only be a couple of 1 mark questions on each. I have heard of students spending hours getting frustrated with cgy & dep but they can't use a whiz-wheel. You need to manage your time and concentrate your efforts accordingly. Your course provider has a duty to cover the syllabus but should tell you where to concentrate your efforts.
Also as suggested above make sure you practise doing questions under examination conditions you are likely to get a nasty shock the first time!