Hey Nebojsa,
i have some tips:
try to relax
do not invent, do tecniques as you know them now
think as if you where practicing the exam, i think this is the most important
and if it helps, one of my sensei sings in his mind so he can relax himself ;-) , and it was an exelent NiDan exam. so find something that calms you down and aikido will flow.
good luck