Hey brother, don't worry. It's easier than you think.
First, it's
short case, and for those who don't know what does that mean; it's about making physical examination
without taking history.
There are 20 marks on the exam. Passing mark (10-12) will be given if you can do proper physical examination even if you stumble and don't answer all of their questions properly. The rest 8 marks is for you and how good the impression you made in the examiners.
They will ask you to do something, then observe how you do it (and I don't totally agree about talking while doing so, coz it can make you lose your concentration. If they see you doing it properly they will know that you know what you're doing).
Then they will ask you about the findings, it's important that you can establish the clinical findings, but never create signs that are not there, miss them but NEVER elicit false signs. Like for example you couldn't notice a palpable spleen although it's enlarged enough; missing a sign that is there can be corrected by experience later on (and they totally understand that) but making up physical signs will make you lose the diagnosis (and important marks). Always be honest with the examiner.
Some tips:

Sunlight, it's important that the examination of anything related to colors (like pallor and jaundice) be done in sunlight, so make sure there's enough and don't hesitate to ask for whatever needed to make the sunlight reach your patient.

Stay cool, it's only an exam, and if you have studied enough; you can answer. Even if you don't know the answer, there's always a chance that you can conclude & improvise (and that's the beauty of medicine) so never fear and always trust yourself.

If you use one; break the
tongue depressor and get rid of it (and show them that you broke it).

Tap on the stethoscope to make sure it's on the right side, looks like acting but imagine that you don't do it and when u want to listen; you find it on the other side!!!.

They say "never back off your opinions" but I dunno, If you only say what you're sure of then it's ok to stay stubborn. Otherwise; be reasonable and if they show you that you're wrong and you get convinced, say something like "sorry, maybe I missed it coz I don't have the good experience, inshalla I'll never forget it"
(They like to play the role of teachers even in the examination).

Practice as much as you can, don't get all messed up into reading and studying and forget the real thing;
the manouver. Passing depends on it, extra studying will get you the extra marks.

They will SURELY make you reach a stage where you say "I dunno". So don't worry if you say it once or twice.

As a dear friend of mine used to say: "There's nothing to lose, only money & pride, being a medical student there's no money, and you have already lost your pride; so there's nothing to lose!" funny, sad but true. (Effective in removing nervousness if you think of it this way; there's nothing to lose)
sorry for talking too much

Bil muwafa8iya