I fell off twice cantering at a dressage show?

They were both stupid falls. I had this really nice dressage horse but his canter was way too fast and I couldn't sit it. I fell off over his neck first, got back on and redid the test and fell off sideways again. I feel so stupid. My canter is usually fine and in the warm up arena we were doing so well and his canter was amazing and the perfect pace. Any tips for staying on next time and for controlling my horse? I feel so dumb I've never ridden that badly.