just since I'm a little slow, "left" means behind you?
when I had this problem in the past, slow down and focus on keeping your torso square to the lanes. By slowing down you should avoid any extra movements, and by keeping your body straight/square your arm should go through its natural swing...
The should isn't really designed to move that direction, so if you can keep your body square that should stop it.
hope this helps some...
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