The noisy environment makes your whistle sound quieter than it really is, so you think you are blowing more gently than you actually are. When you blow harder to compensate for the percieved lack of loudness, the whistle jumps into the upper octave.
Try to avoid sitting next to other whistle players. Then you will be able to pick out your own sound more easily. Of course, try to keep away from anyone with a very loud instrument.