Checking behind w/ set o' jacks on river. Too weak?

[JKDStudent]

Party Poker 1/2 Hold'em (9 handed) converter

Preflop: Hero is Button with J[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/club.gif[/img].
<font color="#666666">3 folds</font>, MP2 calls, MP3 calls, CO calls, <font color="#CC3333">Hero raises</font>, <font color="#666666">1 fold</font>, BB calls, MP2 calls, MP3 calls, CO calls.

Flop: (10.50 SB) 3[img]/images/graemlins/diamond.gif[/img], Q[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(5 players)</font>
BB checks, MP2 checks, MP3 checks, CO checks, <font color="#CC3333">Hero bets</font>, BB folds, MP2 calls, MP3 calls, CO folds.

Turn: (6.75 BB) J[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
MP2 checks, MP3 checks, <font color="#CC3333">Hero bets</font>, MP2 calls, MP3 calls.

River: (9.75 BB) 8[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
MP2 checks, MP3 checks, Hero checks.

Final Pot: 9.75 BB

Results in white below: <font color="#FFFFFF">
MP2 has 8s Td (two pair, tens and eights).
MP3 has Ac 8c (one pair, eights).
Hero has Jh Jc (three of a kind, jacks).
Outcome: Hero wins 9.75 BB. </font>

With a third diamond falling and a board that gives anyone with a nine a straight, I checked behind and took the free showdown. Basically, I was afraid that someone that made something would check since I had been betting the whole time, looking for a raise. I had no reads on these players as we were all pretty new to the table, but given the way they were calling down, I wasn't ruling anything out.

So... was this weak/scared? How bad? And yell at me to make sure I don't do it again.