Just to add, if people are investing here that means they are ready to loose and gain both, which is same with all whether it is a ponzi or gambling site.
Does it?
Maybe it means they believed OP's claim that they
will be able to double their coins.
You made me smile

When you gamble, you're also
able to double your money. For example playing the roulette: bet black, you're able to double your money (but there's 19/36 chance that you won't). I don't think it's a clear scam, but I admit, semantics make it borderline.