Apparently he was given 0.08 first, but then they increased it to 0.2BTC. If this was meant to be hush money, perhaps. I think they felt with the guy though (from the conversations I've seen screenshots of).
Such thing doesn't exist in this space. Casino isn't charity organization. There must be specific reason why player was funded with additional 0.12btc, if it was for a bug then everyone else should also receive 0.2btc, if it is because his plinko win was big then something is wrong here.
I think if the "correct" outcomes from the OP playing the new game would have resulted in the OP having sufficient funds to make the plinko bets up until he won the jackpot, the entire jackpot should be paid out.
If the above is not the case, the floor the OP should receive is what MadZ suggested above. However there are other considerations that would make me believe the OP should receive more, such as FJ essentially "freerolling" their players, and the possibility that the OP may have made different sized rolls had he had a different bankroll size.
I have to agree with you.