Use this lat stretch to eliminate the need to bend your arms in the backswing and try this over the head hip and torso stretch to increase the separation between your hips and torso to make a more powerful swing
Hitting the ball with the bottom of the club face can result from several different swing faults
Focus on your left wrist at the top of the backswing and start of the downswing to get to impact properly, many players have a cupped left wrist which changes the angle of the clubface, this causes an open clubface and results in casting and manipulation during the last portion of the downswing