as someone mentioned already, you should pay those winning bets as well, not just refund what was lost
Of course.
If I bet 1 BTC at 10%, ten times, I'm expected to win once and lose 9 times.
If you just refund the one time I lost when I should have won, and not the 9 times when I really lost, I'm still down 9 BTC instead of being roughly breakeven.
The bets which were settled wrongly need to be settled correctly, not cancelled.