I can't call it gambling , more like a fun timewaster - especially with the prizes  "up to 100 satoshi" 
100k minimal withdrawal makes the players return and play again and again , but it must take a long time reach that amount
its a version of agar.io bitcoin clones , hope it doesn't repeat their mistakes
I'm pretty sure all of the agar clone games are dead because it was impossible to fight cheaters and players who teamed up to kill the opposition and win the prize
if you don't introduce the paid entry system , maybe think of alternative ways of monetizing the site ?
since I am not sure the pay-to-enter model will be too popular