This happened to me less than 1 hour.
I used to play dice with a random altcoin, didn't notice that it changed to btc, hell yeah lost twice about the 1/3 of my balance (it is not that big but hell).
Hmmm i had to recover what I lost, after 2 minutes lost all my balance.
That's why I hate gambling (used to do it with free coins only!)
You have to just cut your losses and forget about it. The best way to avoid losing coins by gambling them away is not to gamble at all. The temptation however may be too much, so you have to keep your coins safe.