Watch this video. http://m.youtube.com/watch?v=psgfJQsgGqY
As the poster above noted, you need to focus on hitting the outside of the ball. You can do this without hitting way out in front, but rather pulling the racquet handle through and making contact slightly past your sternum and be sure to not over rotate your shoulders too soon. That said , you need to be sure you have a good shoulder turn back so you can create the acceleration for your arm to come around. Watch the video and compare it to what you are doing currently.