One of the reasons why you might be hitting the ball thin, that is hitting the ball with the bottom of the club, rather than in the center of the club, is that your ball is mis-positioned in your stance. For instance, if the ball is played too far forward in the stance you might end up having the bottom of your swing behind the ball and then you catch the ball on the upswing, thereby catching the ball with the bottom of the club. If the ball is positioned too far back in your stance, you might be so far forward at impact you can’t catch the ball solidly and you can only catch the ball off the bottom of the club because you are too far forward. To help you find the right ball position for your swing what I would like you to do is the balls on a line drill. First paint a line away from your stance in the grass or just take a tee and make a line in the grass with it. Then tee up four balls on that line very close to the grass. Then, swing at the balls in order but make sure that each time you swing you take a divot. If the ball is too far forward in your stance then what would happen is that the divot would occur before the ball. As you can see when I swing at the first ball the ball is too far forward for my swing because the divot is behind the ball. Conversely, if the ball is played too far back in my stance then the divot would occur too far past the line in the grass and in front of the ball. As you can see when I make a swing with the ball back in my stance the divot starts well after the line. What we are looking for if the ball is positioned correctly is for the divot to start just in front of the line in the grass. As you can see, when I swing with the ball correctly positioned the divot is perfect, starting right in front of the line. This was the correct ball position for my swing, and if you find your correct ball position you will start hitting the ball solidly and not off the bottom of the club.