Your time at the practice range is also useful for checking out equipment. They must have clear repeatable scales, and the mechanism must be tight, in other, words, no slippage. If your sight picture is consistent, the light and wind conditions the same, your point of impact should be the same shot to shot, at least within the confines of the accuracy of your gun. Find out if your pinhead and your post and your crosshair all give you the same point of impact with comparable points of aim. The time to find all this out is at the range between matches.
Some shooters require a sight adjustment between shooting over sticks and shooting offhand.
Although I'm not a master offhand shooter, I have had occasional good days - 7 out of 10 is my best on several of those good days. I am a firm believer in offhand practice. Even five minutes per day at some tiny target in your basement will help noticeably. You'll learn what kind of routine you need. I find that it helps to have eaten recently enough that I don't feel weak from being hungry.