It worked out great, but i wonder if i should just raise the flop, will these slow play cost me in the long term ?

Party Poker 2/4 Hold'em (8 handed) converter

Preflop: Hero is BB with 5, 6.
UTG calls, UTG+1 calls, MP1 calls, MP2 calls, 2 folds, SB completes, Hero checks.

Flop: (6 SB) 6, 6, 5 (6 players)
SB checks, Hero checks, UTG checks, UTG+1 checks, MP1 bets, MP2 calls, SB calls, Hero calls, UTG folds, UTG+1 folds.

Turn: (5 BB) T (4 players)
SB checks, Hero checks, MP1 bets, MP2 raises, SB folds, Hero 3-bets, MP1 calls, MP2 caps, Hero calls, MP1 calls.

River: (17 BB) 9 (3 players)
Hero checks, MP1 bets, MP2 raises, Hero 3-bets, MP1 calls $12 (All-In), MP2 calls, Hero calls.

Final Pot: 29 BB