Ideally to fix both the issues you would want the streamer/mods to have the option to retake the points back to redistribute the points in the case of selecting the wrong result.
For cancelling your prediction, as long as it is within the 2 minute or whatever length vote time set by the prediction, I think you should be able to cancel your vote. If it is after the vote period ended then tuff luck. You wouldn't want to let people cancel after the vote as people can just cancel to get the points they were going to lose back.
Ideally to fix both the issues you would want the streamer/mods to have the option to retake the points back to redistribute the points in the case of selecting the wrong result.
For cancelling your prediction, as long as it is within the 2 minute or whatever length vote time set by the prediction, I think you should be able to cancel your vote. If it is after the vote period ended then tuff luck. You wouldn't want to let people cancel after the vote as people can just cancel to get the points they were going to lose back.