NL5 QT outsuit - Failed bluff.

PokerStars - $0.05 NL (6 max) - Holdem - 6 players
Hand converted by PokerTracker 4

Hero (SB): 137.4 BB
BB: 100 BB
UTG: 108.8 BB
MP: 102.4 BB
CO: 108.8 BB
BTN: 175.8 BB

Hero posts SB 0.4 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.4 BB) Hero has Q♠ T♣

fold, fold, fold, fold, Hero raises to 3 BB, BB calls 2 BB

Flop: (6 BB, 2 players) 8♥ 7♠ 4♠
Hero bets 4 BB, BB calls 4 BB

Turn: (14 BB, 2 players) A♥
Hero checks, BB checks

River: (14 BB, 2 players) 3♣
Hero bets 12 BB, BB calls 12 BB

Hero shows Q♠ T♣ (High Card, Ace)
(Pre 42%, Flop 30%, Turn 14%)
BB shows 8♣ K♣ (One Pair, Eights)
(Pre 58%, Flop 70%, Turn 86%)
BB wins 36 BB

I knew he didn't have an ace because he didn't bet the turn.

Is this a bad bluff?

Why or why not?