The main thing is to not get too uptight and nervous (as easy as that may sound) all he is looking for is general safety, if your radio, general handling and landings are good you will have no problems.
The nav is as hard as you make it, but again you have to really screw up to fail on the nav i.e get totally lost and panic and not rectify it. Personally I'd would not have booked a test until you was sure you could nail the nav no problem just to make sure.