Derailer extension pivot

Received my Prime. Assembled it and noticed derailer was up againt the frame. The bolt holding the extension was not very tight and had pivoted up. I pushed it down away from frame and tightened. On my first high speed run using throttle it pivoted up again causing chain to come off and damaged my frame. Think the derailer may be damaged. Disappointed. Dont think I can tighten it anymore without breaking it.