Button aggression - line check

Opposition is an unknown. Have been playing solid and haven't been bluffing much. How is my line here? Was I too weak? Too aggressive?

Cryptologic
No Limit Holdem Ring game
Blinds: $0.25/$0.50
5 players
Converter

Stack sizes:
UTG: $39.35
CO: $57.90
Hero: $76.31
SB: $62.90
BB: $50.20

Pre-flop: (5 players) Hero is Button with
2 folds, Hero raises to $2, SB calls, BB calls.

Flop: ($6, 3 players)
SB bets $1, BB folds, Hero raises to $4, SB calls.

Turn: ($14, 2 players)
SB bets $1.5, Hero raises to $6, SB calls.

River: ($26, 2 players)
SB checks, Hero checks.

Results:
Final pot: $26

Raise flop harder then check behind on turn.

looks ok to me, although i'd raise just a bit more on either the flop or turn, maybe even both.
seems like this opp will just call down with QJ type stuff, as long as it's a reasonable amount.
in other words, it doesn't look like someone who's gonna bluff 3bet if u raise small like this, but that's something to consider.
i'd more likely call then raise vs someone thats moderately aggressive. not sure that's the best, but getting 3bet would suck.