Villain 1 CO ($7500)
Villain 2 (SB) ($2000)
Hero (BB) ($1200)

CO has been playing ~50% w/ 20% 3B
SB raising ~10% of limped pots
Hero -- probably seen as spot, never played in this game before ~20% VPIP

CO has been winning every pot >500$

Earlier hand saw CO w/ J726xxxx check/call two pot bets on Jh 6h 5 8h 6 board, and then Pot call the river vs. AhQhxx

8 handed game

Preflop
CO limp
SB raise to 20$
Hero (5c6c9h10h) call
CO call

Pot: (60$)

Flop:
2d3h4c

SB bets 60
Hero ?? (called)
CO raises pot (300$)
SB folds
Hero?? (Pot 600$)

Felt at the time that it was an obvious GII spot? Is the flat postflop a mistake?

thx