[Wish]

300 had been getting a bunch of folds early in a $3 rebuy? How strange. Most of the time in one of those, you could just open-shove preflop and get a call or two. In a rebuy like this, I'd check/fold the flop. If you'd gotten one or two callers there's a chance that none of them has an ace. With 5 callers, somebody's got the ace, and they're never, never, never folding it. If you're going to bet, half-pot is fine. It accomplishes everything that a pot-sized bet would. You'll either fold out everybody (unlikely, but possible), or you'll get looked up by somebody with an ace (and quite possibly somebody with something ridiculous). As played, absolutely fold the river. I think there's zero chance you're good any more. Somebody's got an ace, and the 4 just filled a couple of straight draws as well.