The vans are indeed huge and if you haven't ever driven a van you need to be aware of its size. Dont swing out on turns that isnt going help unless you know how to do it correctly. When making a turn you need the front end to go deeper into the junction before making the turn, remember the back wheels will always take the shortest route.
Try and keep an eye on your left mirror as you turn left so you can see where the back end is going in relation to your turn. Same goes for a right but if there is no one in the junction you have a bigger margin of error.
Make your instructor/assessor aware of your inexperience as much as they are there to assess you they are ultimately teachers and will help you more if they know they need to. Biggest thing to remember is to take your time, its much easier to fix something thats going wrong because your going slowly that it is to fix something thats gone wrong because you did it too quickly to be able to stop it.
The assessment is more or less in three parts an initial drive to give you time to settle in, the assessment and then the fix the trouble is its still all an assessment get it wrong badly in the first 30 seconds and you'll still fail. So as I say take your time relax as its not a test its pretty much is this guy an idiot / dangerous if yes
fail if no
pass with feedback on where they can improve.
My comments are my own and represent my opinion only not that of any person or company I may have links to.