Maybe I do things wrong, but all I do, to tighten the cam sprocket, put the belt on, set your timing, tension the belt, then I have an assistant hold the crank while I torque the sprocket. Rotate the engine around a few times, check your timing etc. Never ever failed to work, nor ever had a problem. Trying to tighten that sprocket without a belt on it, or some kind of holder is indeed asking for trouble. Sorry about your luck. I'm sure you will fix it and have a beautiful car to drive. Enjoy!!