preparation on the firing point

[tbonesmith]

Here's my take on it, and I've been there too.
Until you have your own rifle you're on faith as to how the rifle shoots, nothing you can do so don't worry about it at all.
You're not going to win anyway as you're learning so start by focussing on the basics, position, breathing, consistency of trigger pull, consistency of cheek weld, consistency of sight picture.
There are lots of good articles on this site about marksmanship, read them and apply what you can.
What you absolutely can control regardless of whos rifle you're using is your position, sight picture, breathing and trigger let off. If you get these under control your scores will increase. If you don't worry about what you can't possibly control and focus you preparation and efforts on what you can control, you may be less flustered and more able to do the business.
One technique that I've found helpful in the past is to run through the shoot in your mind the day before in detail... go to the mound, lied down, adjust the sling, find your natural point of aim, take 2 dry fires, organize you ammunition, is my scope set up?, load a round, breath in, out , in, out , in, half out, find the sight picture, take the first pressure, squeeze off the round, watch for the fall of shot , relax, make adjustments, breathe... for the entire shoot, then you feel really mentally prepared for the shoot as you've kind of done it before.