Ok, flying along on a nav/diversion excercise, overhead Auchterarder, and instructor gives diversion to Kinross. I make the necessary calculations, and set off on my new wind corrected heading (we're taught Maxdrift technique). However, the instructor then comments that something's amiss as we're probably about 15deg off with a visual check. (Not being particularly savy with the area, I didn't realise that Kinross was that town just beside loch leven

)
Can I just make an instant track correction, and say to the examiner, "I've obviously made an error here", or should I assume no local knowledge, and read map/ground, with an adjustment at the half way point?
I'm struggling to get regular time in the air, and it would be good to here some comments on best practice, just to keep things fresh in my mind. My instructor has recently left to work with a local airline, and I guess it's going to be even trickier to get slots now.