How can I correct my swing path from naturally going outside-in?
Many golfers are trying to swing squarely down the target line, not realizing that their bodies are turning at the same time. So by the time the club reaches the ball, this turning motion changes the swing path from square to outside-in without the golfer even realizing it. What I would recommend is doing the two club warmup drill slow and easy like a baseball player in the on-deck circle. While you are doing this repetitive drill, you should be able to stare at a spot on the ground where the club passes over, and see the real path of the club AS IT PASSES OVER THAT SPOT, and make corrections to that path. Here is how to make those corrections:

Instead of trying to swing down the target line, try to make your downswing inside out. If the target line is twelve o'clock, make your swing path toward one o'clock because your body's turning motion will change your path to twelve o'clock without you realizing it. Also extend your follow thru to one o'clock and exaggerate that. If you quit the follow thru too soon, you are promoting an outside-in motion.

Be careful not to take your backswing to the inside because that might cause a loop to the outside on the downswing. Take the backswing straight back and high like Sergio Garcia, and then watch how Sergio attacks the ball from the inside. (see www.geocities.com/golfwithjoey)