Don't worry about nerves, the examiners don't want you to fail, some will be nicer than others but in general they'll know how you feel! Just focus on the road, the nerves made my adrenalin kick in which actually made my decision making a bit better!
As for the roundabout thing, usually you should exit a roundabout in the left hand lane, enter the roundabout in the right lane if you are turning right, check your mirrors for any cars in the left hand lane after the 1st/2nd exit, and if it is safe move to the left, if it is not safe then the car behind you has probably made a mistake and you'll just have to exit in the right hand lane, no harm done.
When it come to stalling, try lowering the clutch a bit and rev a bit more, it may make a noise but theoretically should make you move away. With a new car it always takes time to adjust, after passing my test i bought myself a car and it took several weeks of driving before i adjusted to the clutch control etc.
Good luck.