Skill tests do not have to be booked in advance. I notify all of mine at the end of the month. CPL and IR are the only exception as they are done through flight test bookings.
I am generally booked one or two days in advance of the test.
Just relax, as an examiner I am taking a snapshot of what your Instructor has taught you and no Instructor puts forward a candidate they think is not ready.
You are taking me along as an observer, fly the aircraft as you have been taught and you won't have an issue.
It is very rare to have to fail a candidate although we get the occasional partial if they have a brain fart.
As I said, just relax, don't overthink it and prepare properly. We are not there to fail you or catch you out.
Enjoy the test, it will be a memory that stays with you through your flying career as a major landmark.