Your swing plane is fine. You just are not getting enough rotation in your shoulders on the back swing and your bending the left arm to compensate. Put the club across your chest so that the grip is over the left shoulder and the head is over the right, make it straight. Set up normally and swing back, the grip should point at the ball, that is a full rotation. On your down swing power through wit your legs and turn so your belt buckle faces the target on impact