Walao.. over corrected.. ;p Maybe is because during the test blur blur, the car didn't centre and you thought you needed correction but actually not required?
During my vertical parking practice also.. I went through the first few times swee swee, vehicle in the centre of the lot, then one day I was quite tired (IPT the night before and I got stiff shoulders), the car went off one side, sighting point correct but the turning was late.. Then I realised that I just turned my head instead of my body which I did all the time to look at the rear windscreen, so sighting point is off.. It's makes quite a difference for vertical parking because the lot is just nice for Civic. Got to be quite precise.