How stupid was this?

[Mez]

So... feel free to flame away. Looking back this play was really an unecessary steal.

$80 buy in, with a $20 cash headhunter bonus
10 people started with 3,000 each
top 3 get paid, 3rd is $100.
5 left, blinds 300/600.

I'm 2nd in chips with 5.5K. I have a very tight image after not playing a hand for the first 2 levels and have only pushed twice - once w AA preflop and another time after flopping top pair and I was very short. I won both pots.

Sitting to my immediate right is chip leader with ~18K. He is loose aggressive and willing to outplay me (specifically - I'm uber tight) in any pots.
Button has 1K
SB has 3K
UTG has 4K

UTG folds, I have K9o. I push.

Clearly I was just trying to steal blinds - under 10xBB. Clearly I was called by a monster and lost. Really think this was a mistake given the landscape of the chip stacks. Thoughts?