First I would like to clarify that this problem is not in our system but rather a general Bitcoin network problem where duplicated conflicted transactions are being broadcasted.
You will notice that one of the transaction will confirm by the Bitcoin network normally and the other one will be canceled.
Simply ignore the duplicated canceled transaction. It will never confirm by the Bitcoin network and no funds will be deducted from your wallet for it.
Consequently no payout will be issued for the duplicated canceled bet transfer.
So the bottom line is, you can continue and bet normally and ignore the unreal duplicated conflicted transactions.
For the purpose of the competition, only one of the bets (the real one) will be counted.