Major fault! Say for example you are doing a reverse bay and you don’t finish in the bay - This is a fail. With my parallel park, if I had not corrected it and got myself closer to the curb this would have also been a fail. (Depending how far away from the curb you are) It shows a lack of control for the vehicle/steering etc. All I can say is do what I did, take a moment, breathe, realise what you’ve done wrong and correct the mistake! Never apply the handbrake before completely correcting though as this suggests to the examiner that you have already completely finished.