72 Van, is there any way you could get hold of a tester? If so, would you be able to test your home/flat and on a regular basis? I used to be like you with testing but doing it as often as you can will remove a lot of hesitancy and give you confidence which is most of the battle. Those examiners want the right answers delivered with confidence otherwise they might think you guessed it..
Repetitive and correct practice of procedures won't be all that you need, but it helps because it'll free up your thoughts a bit on that orrible test rig. I know this from just having completed my AM2. The worst feeling as you seem to understand is trying to go in there imagining what you have to do and why.