If it makes you feel any better, I fell off during my second ride yesterday too. My circumstances were a little different--

I was coming up behind a stopped car at an intersection, unclipped my left foot early (letting it hang down) and slowly coasted towards the intersection. Then the car got the green light and started to roll forward, so I put my left foot gently on the pedal and started to accelerate again; I didn't even intend to clip in, and just pushed my left foot down on the pedal to keep things moving. This turned out to be a big mistake.

Shortly after the car started rolling, it stopped for people in the cross walk. I went to put my left leg down and come to a complete stop when I realize it's half-clipped in/snagged on the pedal and then... down I went.



It's amazing that while on my trainer while I was first learning, it was hard to get my foot in, and here I was inadvertently doing it without thinking. *sigh* Now I know that if I want to push my left pedal along while unclipped... I'm doing it with the center of my foot, not the ball where the cleat it.

Also, as the others have mentioned, I think unclipping both is unnecessary, just make sure you tip the bike (it helps to turn the wheel too in the necessary direction) as the unclipped foot.

Happy riding!