No raise pre-flop. How bad is it?

[Octopus]

Party Poker 1/2 Hold'em (8 handed) converter

Preflop: Hero is SB with 9[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/heart.gif[/img]. MP2 posts a blind of $1.
UTG calls, UTG+1 calls, MP1 calls, MP2 (poster) checks, CO calls, Button calls, Hero completes, BB checks,

Flop: (8 SB) 9[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/club.gif[/img] <font color="blue">(8 players)</font>
Hero checks, BB checks, UTG checks, <font color="CC3333">UTG+1 bets</font>, <font color="CC3333">MP1 raises</font>, MP2 folds, CO calls, Button calls, Hero calls, BB folds, UTG folds, UTG+1 calls.

Turn: (9 BB) 7[img]/images/graemlins/club.gif[/img] <font color="blue">(5 players)</font>
Hero checks, UTG+1 checks, MP1 checks, CO checks, Button checks.

River: (9 BB) 6[img]/images/graemlins/spade.gif[/img] <font color="blue">(5 players)</font>
<font color="CC3333">Hero bets</font>, UTG+1 calls, MP1 calls, CO folds, Button calls.

Final Pot: 13 BB
<font color="green">Main Pot: 13 BB, between UTG+1, MP1, Button and Hero.</font>

Pre-flop: It never even occured to me while playing this hand that I should raise pre-flop, but now looking back it seems like a good choice. How bad a mistake is this?

Flop: I decided to try for a check-raise to try to move out any gutshots (or better backdoor flush draws, for that matter). Since I had no clear idea who might bet, should I have just bet out? Would anyone have 3-bet it?

Turn: I check and plan to fold.

River: I bet and plan to pay off any raises.