Before the test route

I had driven around the test centre every evening until the junctions were familiar. Yet, seated beside the examiner, I saw the same road as a succession of places where I might choose the wrong lane. He entered details into his tablet while the clock clicked behind us. I adjusted the mirror, although my instructor had checked it only minutes earlier, simply to give my hands a task. Each second of waiting allowed another possible mistake to occur to me. When the examiner eventually asked whether I was ready, I was almost grateful: beginning seemed easier than imagining it.

In your own words, explain the writer's thoughts and feelings before the driving test starts.