What would you do? #49 - KK vs. TAG 3bet PF, facing large turn bet

Full Tilt Poker $0.25/$0.50 Pot Limit Hold'em - 9 players
The Official DeucesCracked.com Hand History Converter

UTG+1: $50.00
UTG+2: $17.95
MP1: $26.90
MP2: $84.90
CO: $63.65
BTN: $6.00
Hero (SB): $106.95
BB: $61.65 - 15/7 @ 750 hands 2.8% 3bet
UTG: $41.70

Pre Flop: ($0.75) Hero is SB with Kc Ks
2 folds, UTG+2 calls $0.50, 3 folds, BTN calls $0.50, Hero raises to $2.50, BB raises to $8, 2 folds, Hero calls $5.50
Should I be going broke here? Should I be 4 betting with 120BB effective stacks?

Flop: ($17.00) 3d Ah 7c (2 players)
Hero checks, BB bets $10, Hero calls $10

Turn: ($37.00) Td (2 players)
Hero checks, BB bets $21, Hero folds
Too nitty? AA or AK?

Final Pot: $37.00
BB wins $35.15
(Rake: $1.85)