Shootaway,
For off hand shooting and more specific, match type shooting, you are somewhat correct in your hold, but much more to it. Your rifle is heavy, some 10lbs+ and so are match rifles. AR15's near twice that for match shooting and to stand erect forces you to "muscle" the rifle while breaking the shot. That is a "no, no." Don't stand facing the target, but rather sideways and spread your feet as wide as your shoulders, rotate at the hips and lean backwards a bit. Draw an imaginary line from the tips of your feet to the target. This helps establish your NPA(natural point of aim.) Depending on left or right handed, place support elbow on hip. Having leaned backwards and elbow on hip serves to steady your hold and improves center line of gravity so to speak and weight of rifle less of a burden by doing so. By doing this you lessen the use of muscles and utilize skeletal support. Muscles are similar to springs and tend to flex/tire whereas the "bones" do not. Once you have lined up on target, shut your eyes for a count of 5 and then look at target and note where the muzzle is pointing. If you are off one way or the other, move one of your feet (depending on right or left hand shooter) only!! Right handed shooter would use his left foot as anchor foot and must not be moved. If you are off to the right of target, move slightly your right foot forward and take another 5 count look. By doing this you have moved muzzle to the left or corrected your NPA. Opposite if muzzle is pointing to left of target, move right foot rearward a bit. Now that you have mastered left and right, what about elevation? Just because you started with your feet spread to shoulder width does not mean that has to remain. If you close the distance between your feet you have gained elevation, widening the spread will lower elevation. I repeat, it is critical that you do not move your "anchor" foot or all bets are off and you have to start over again. Do the 5 count more than once and key to this is that as your muzzle "wobbles" it will generally be within the target area and that is what you are trying to achieve. No one can hold the rifle perfectly still on target for very long and you have to learn to accept the wobble. It is said that most wobble in a horizontal figure 8 and trick is to break the shot when the muzzle is wobbling toward the center of the target, not away from it. Assuming you are holding your breath while shooting, consider "catching" your breath in your throat, not your mouth for to do so adds pressure to the weld/cheek point on your stock and can cause shots to go astray. Might also add that to hold your breath more than a few seconds, 5 or so, vision begins to blurr. Take the rifle down and cradle it if the sight picture does not look good and breath to restore yourself. Sounds complicated and tedious, but with practice becomes natural and would suggest you take 10 shots at 200yds using the above and see how you do. In matches you have 10 minutes to take the 10 shots which is a lifetime, but don't rush it starting out, it will come to you quicker than you think. There are those who sight in their rifles off hand. Suggest a target face of some 24" in diameter with black of 13", std. SR target, and try 10 slow fire off hand shots and then move closer to 100yds. Believe your shooting will improve by this exercise be it target shooting or in the field. Anything that builds your confidence will help you whatever you are shooting. Google a Mr. Jim Owens and buy his books, very good primers for those wanting to improve their shooting skills.