Mahmoodnz,
before you sit the next test get a copy of what the requirements are, and what the allowances are.
I believe they state that for an approach -0ft +50ft of MDA. If this is the case don't fly down to minima. fly +20 ft or so, that way you have some fat built in to it. Same as approaches, and arcs. If you know what your limits are you can help reduce your stress levels, but don't be complacent with being +1/2 mile off track, or 1/2 dot high. It just gives you the knowledge that you wont fail being in this position
IFR is a different type of flying than vfr and i was confused by it at first but once you understand it and fly it more often it becomes 2nd nature, actually it is easier than VFR as you're told when to change radio frequencies, and cleared for approaches etc etc.
Best of luck with the next test. put in the hard yards, and pass. It doesn't look good failing to much! I use to struggle with stress leading up to flight tests. Find a way to deal with it,be it exercise, or chilling out before the test. Because in this industry you're always having flight tests, exams, and medicals.
Good Luck, and let us all know how you do.