Hi Phsyio1992.
What is very cool is that, in saying this, "The GMAT feels like a moment of judgement which decides whether I am intelligent and good enough for the master program at the university," you have summed up exactly what is going on with many people who are anxious when they take the GMAT.
They have the impression that their scores will prove something about them for once and for all.
Fortunately, that whole mindset is based on a key false belief, that you are the way you are and will be that way from now on.
That mindset is called a "fixed mindset," one that involves having the impression that how you are is fixed.
It's not.
Your intelligence is not fixed.
Your "OCD" situation is not fixed.
Your GMAT skills are not fixed.
The truth is that you can develop yourself continually, and that you can score as high on the GMAT as you want. So, all your GMAT score indicates is how skilled you are at a point in time. Nothing else.
I know someone whose first GMAT practice test score was 380 and whose last score, on the real GMAT, was 750. She was worried about how "smart" she was too.
So, there's nothing to be anxious about. You can certainly score 450, and you could score much higher with more preparation.
Doing so is just a matter of developing skills.
The more clearly you understand the foregoing, the more you will have, rather than a fixed mindset, what's called a "growth mindset."
Here's more information on having a growth mindset.
https://www.mindsetworks.com/science/