The suggestion above on putting dummy rounds is good. For your Beretta, you can mix in dummy rounds in the magazine (like the previous poster said, have somebody load it so you don't know where the dummies are).
Your problem might be recoil anticipation. Either you don't know what to expect on your first shoot so didn't react in time to mess it up or the double action trigger might be very smooth to make the shot a real surprise.
Another thing to try is to watch your front sight and see if you can see muzzle flash when you fire. You should be able to see it under most conditions.