There is a reason it does this. The stick works okay, not perfect but okay...you have to learn how to work with it.
This happened to me the first few times I started using analog to pass. The thing I was doing was I was holding on to the stick too long. That is, I push it out to the direction I want to for power but then, I pull the stick back to end the power bar. Well when you pull the stick back you pull it straight into the opposite direction...the bar is full, then the games thinks you want to hit in the opposite direction (the one it sees last). What you are supposed to do is, tilt the stick where you want it to go, when you are done with it, release the stick (gently) and watch the ball fly to where you put it. Remember it is on a spring mechanism, it will go back to it's original position without your help.
Try it in training first. A lot of people try it in games expecting big things to happen...in a game you are under pressure, the defence is slicing at your feet...in training you can practice doing it without pressure. When you are good, then you can do stuff in a game.