when trying to throw it hard, you may be bringing the ball back too much by muscling it, and there for you bring your head back with it. when that happens, you are either going to pull through it miss it left, or you will lead with your shoulder, causing the ball to Gorki. try slowing down a bit like someone else mentioned.

one thing i do, is i actually move 1 step back in my approach to shoot the 10-pin. this way my feet are not ahead of the ball as much, and so i won't want to pull through the shot.

what do you look at when shooting the 10-pin? you may be looking too far left as one person mentioned or even too early on the lane.  you could try looking farther down lane. by doing that, it will help keep your head on your mark and not want to bring the ball back so far. you will still generate speed on the ball, but will have more of a relaxed armswing, instead of feeling like you have to place it in order to pick it up.

like someone else said "practice until you get it right". but one thing i have noticed, is that when you find something, stick with it. just because you miss one, doesn't mean you have to change what you are doing. also, keep a positive mindframe. if you think negative when shooting it, you will get negative results.
we are only human. unless you are Walter Ray, who is the man when it comes to the spare game.  Good Luck and let us know how it is going.