I think this is reason why you reduce the max allowed amount per bet, I tried 2days ago and I could still play with 100coins per bet but now I cant play with 100coins per bet as it is now limited to 50coins per bet.
You are giving away decent amount of money for free, why dont you try to make a better contest with bigger prize where players need to play with real money?
If you want to do it, make sure to escrow the prize. Although you started here since few years ago, but escrowing the prize will make it better and no one will doubt about it.
Anyway, how much is your budget for the free $100 promotions? How many winners left you are going to pay?