I would contain the arm "Player" Object into an empty object which center 0,0,0 were on the exact end of the pen. (Sorry if my English isn't good enough :p) Then every time the player press an arrow set the position of the empty to the center of the circle.
Now... I think that the main problem is that the points aren't on a vertical or/and horizontal direction. You need to set some rules about what Up,Down,Left and Right mean.
Hope that helps.
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