It is normal that you fall while you are learning. Do not fear. I've been using clipless pedals for a month or so and what I do when I approach those technical parts of the trail is that I twist my feet and partially unclip by letting the front part of the clip on the pedal, that way I get the almost the same efficient pedaling power but I can put my feet on the groun if I need to.

Bottom line: it is just a matter of practice.

Hope this helps,

Ricardo