Hi Dan. You aren't the first person to miss the route up Narnain - the start is a bit overgrown and its easy to go wrong. I'm confused by which car park you were at though! Well done on making the summit.
Have you had a look at the
Skills and Safety section? If you read through the first four of the navigator's dozen skills you might start to get an idea on the use of a compass - which is essential to pick up really. Then have a go at making sense of it on a decent day.
Many of the guides listed on site also offer in depth navigation courses which are well worth it, but the MCofS offers cheap (£25) short navigation courses which are another good option - but they are done for this year as it will be winter skills soon