I had problems with keeping my GPS running (the powerpack I was using was faulty) so mostly navigated via the arrows or by riding around enough people that I rarely had to think where to go (just follow the 10 or so people you can see ahead in the distance).
Ironically when I did get the GPS working again (near the end) I was in a bit of a demi coma state and slavishly followed the pink line, but that happened to be the route going out from the start. I only noticed after 5 minutes as there was an absence of other riders or arrows but didn't bother to backtrack and rejoined the official route a few km from the finish. Nothing bad happened, my ride was still homologated.
I was more annoyed that I didn't record the full ride on my GPS. I like data.