It is impossible to tell the exact path of the club without some sophisticated launch monitor technology, but you can get a fairly reasonable approximation by looking at ball flight. Sometimes, it's hard to believe (or feel) the swing that you are actually making so it's good to use objective feedback. The gate drills can be very useful for that, but you can also use a less obtrusive method if you set up a station like the one demonstrated in this video. You are going to check the path of the club at shaft parallel to the ground in both the downswing and the follow through. This is the time when your club should pretty much follow a plane, so you can get an idea as to how far in to out or out to in the club path is swinging by comparing the club head to the hands (or alignment sticks) at these two check points.