In an attempt to lift the ball in the air, you unhinge your wrists prematurely as you swing down (inset). It's known as "casting," like a person slinging a fishing line, and this unhinging of the wrists promotes an over-the-top swing and weak, scoopy impact.
Solution: hold it back. Take the club back with both hands, and then hook the shaft with your right index finger. As you swing down, keep the hinge in your left wrist by resisting the swing with your right index finger (above). When it's time to hit shots, remember this feeling of resistance in the transition.