6$: Heads up with A9

[Jack-in-a-box]

My opponent is an average player. Should I have went allin preflop? How is my flop play?

PartyPoker $6 Regular Tournament, Big Blind is t200 (4 handed) Converter on pregopoker.com

CO (t4850)
Button (t5760)
Hero (t2720)
BB (t6670)

Preflop: Hero is in SB with A[img]/images/graemlins/spade.gif[/img] 9[img]/images/graemlins/club.gif[/img]
<font color="red">Hero raises to t500</font>, BB calls t400

Flop: (t1200) K[img]/images/graemlins/diamond.gif[/img] 9[img]/images/graemlins/spade.gif[/img] 2[img]/images/graemlins/club.gif[/img] (4 players)
<font color="red">Hero bets t2120 (All-in)</font>...

Thanks