If you accidentally go the wrong way, don't worry - the instructor is primarily testing you on safety so if you accidentally end up in the right lane and can't pass across safely tell your examiner this and as a result you cannot go in that direction. Then carry on as normal and he will give you a new route.
Do this so you go round and round in circles on a pre-determined route you know and can do
job done 
Just be confident and drive smooth. I should have failed mine for clipping a kerb while pulling up and pulling out too close to another car. But I passed because the rest of my driving was very good 