You have my sincere sympathy!!! I used to use a slingshot to keep the neighbor's cows from busting down my fence posts, from rubbing on them in the spring when they began to loose their winter coats. I would not think it would take that much aiming to hit a cow!!!
O.K. ... that was a bit snide of me, but I just could not resist.
I do have a whole lot to say about aiming ... plan to write a piece about it ... but will try to give you the quick and dirty right now. This is how I do it with any slingshot, including the wrist braced ones, of which I have several.
1) Stand sideways to your target. I will assume you are right handed and hold the frame in your left hand. So there should be a line coming from your target, through the arches of both feet. Your feet should be shoulder width apart or even a little more. This stance will allow you to get a full draw all the way across your chest.
2) Hold the frame sideways in your left hand, arm fully extended at shoulder height ... line through the forks perpendicular to the ground, handle parallel to the ground.
3) With ammo in the pouch, grasp the pouch with a guitar pick hold ...thumb mashing down on bent index finger, pouch between, thumb facing up.
4) Pull your right arm as far back as you can, bending your elbow in the process. Your right fist will be about even with your right shoulder.
5) Turn your head to face the target.
6) Bow your head forward toward your chest, face turned toward the target, until your cheek just kisses the top tube.
7) With your peripheral vision, check to be sure the tubes are stacked on top of each other.
8) Sight along that top tube just like you were looking down a broom stick or a rifle barrel (I am assuming you are right eye domminant.) Personally, I close my left eye to get a clear sight picture.
9) Focus on that front fork, just like when shooting with open sights. Use the middle of the tube on the front fork as your sight ... place it where you want to hit the target. For adjustments, move your body at the waist, not your arms nor your head.
10) Gently release the pouch.
Sounds like a lot, but after about 10 or 20 shots, it will become more automatic. If you have done everything right, your ammo should strike somewhere in a vertical line passing through your target. That is, you may be a bit high or a bit low, but you should be right in line. If you are a bit high, you probably did not bow quite enough ... honor your target ... bow to it! If you are a bit low, then your need to aim a little higher on your target. To aim higher, bend sideways at the waist, rather than just lifting your left arm. If you are hitting consistently to the left or the right, rotate your left wrist to bring the point of aim into coincidence with the point of impact.
Shooting a slingshot is not all that different from shooting a rifle ... but the sights are just a little different, and I take more of a sideways stance in order to get a full draw.
Try it ... practice it for about 50 or 100 shots. It works well for me ... but all of us are different, and you may well find something else that works better for you.
Cheers ... Charles