Hi @RenataW. You are probably now over the first stage with the scan. Well done.
You are right that the thoughts going around in your head are your worst enemy. Try to stop those a bit by thinking over yourself - as soon as a thought appears wipe it away with a pleasant thought (this could be the same one each time) or simply telling yourself sternly "stop". It does work.
Once you are in for the surgery tomorrow I reckon "the system takes over" and it is out of your hands so you can just relax and let the specialists do their job and take your worries away.
We are all thinking of you and wishing you well for your surgery tomorrow. π