A little tip
The GST is YOUR flight and the examiner will want to see you handle it as so. It's down to you to do the W&B, the runway length checks and everything else.
The catch is, they may well be giving you tips whilst you are flying so it can "feel" like it's not really your flight and you'll lapse into "training mode". That is what will lead to failure. Make sure you continue the FREDA checks, handle the RT and at all times act like it is your flight.
The only thing about aviation is, even though it's taught as a science, it's anything but. You may even find things that your instructor has taught you but your examiner disagrees with. Even now I see 2 very experienced pilots flying together, they will disagree with each other. So if your instructor disagrees with something you are doing it is NOT the end of the world, and it doesn't mean that you've failed.