If it was a true AK-47, then it has a full-auto select-fire trigger. You may have had the selector lever only half-way down in the full-autop setting.
My guess, however, is that it was a semi-automatic AK clone. In that case, it sounds like you may have been jerking the trigger or uninentionally bump-firing the trigger. The other option is a malfunction of the fire control group, but since you said this only happened with you firing it, we have to assume it was the shooter.
The standard "Warsaw-length" stock of an AK can be short for a lot of taller Western shooters. However, I am 6'-1" with long arms, and I find that I can acheive proper cheeck weld and sight alignment by holding the butt of the stock about 1.5"-2" closer to the center of my body than I normally would. It's also easier to shoot an AK with your body more "squared-up" to the target.