Difficult flop decision with 99 deep stacked

My biggest loss tonight......Did I play this hand correctly?




Poker Stars, $0.10/$0.25 No Limit Hold'em Cash, 9 Players

BTN: $26 (104 bb)
SB: $32.23 (128.9 bb)
BB: $25 (100 bb)
UTG+1: $25.10 (100.4 bb)
UTG+2: $25 (100 bb)
MP1: $27.89 (111.6 bb)
MP2: $36.11 (144.4 bb)
Hero (MP3): $38.34 (153.4 bb)
CO: $59.39 (237.6 bb)

Preflop: Hero is MP3 with 9 9
3 folds, MP2 raises to $0.75, Hero calls $0.75, CO raises to $3.50, 3 folds, MP2 calls $2.75, Hero calls $2.75

Flop: ($10.85) 7 8 6 (3 players)
MP2 checks, Hero bets $5, CO raises to $10, MP2 folds, Hero raises to $34.84 and is all-in, CO calls $24.84

Turn: ($80.53) 2 (2 players, 1 is all-in)


River: ($80.53) 7 (2 players, 1 is all-in)

Results: $80.53 pot ($2 rake)

Final Board: 7 8 6 2 7
MP2 mucked and lost (-$3.50 net)
Hero showed 9 9 and lost (-$38.34 net)
CO showed K K and won $78.53 ($40.19 net)