Hi,
Unfortunately like trying anything new (driving a car, playing guitar) it seams impossible at first and you think you will never be able to do it. Brushcutter has covered it but practice is the best method to get better, as previously mentioned getting the balance right to get horizontal cuts is tricky at first. We balanced a tennis ball on the bar, just get used to how the saw feels horizontal. When doing felling cuts, if you are allowed you could try to start with a high stump then once you have felled the tree you still have a few feet of stem left. You can then have another practice at a face cut and back cut on the same trunk. Moving the bar away and towards yourself during the back cut can also help to see your progress and you will have a better chance of meeting your face cut parallel.
Also read the notes and the assessment questions and practice the chainsaw maintenance over the weekend. You will feel much better going into the felling if you haven't had to sweat and be constantly prompted through the questions by the assessor.
Good luck, you clearly care about getting it right so you will be fine.
Also look at all the thickos on here who have passed (myself included) it can't be that hard
you got this.