was I a fish at this aztec rounders step 3?

[Skipbidder]

I've recently been playing Rounders (at Aztec Riches). They have different names on other Prima skins.

Formatting for this question is terrible, and I apologize. Feel free to send me flames in private messages.

Buyin for a Round 3 is $123.75
Ten players.
First four places pay $302.50
Fifth pays $27.50

Assume the following situation (which roughly happened fairly recently...I don't have the hand history to give exact numbers)

Down to last five players.
We have the small blind.
Before posting,
SB (us) 6 BB
BB=7 BB
UTG=15 BB
CO=4 BB
Button=18 BB

Button has been the most aggressive player at the table, raising quite a bit and taking down hands uncontested. He has played over the top of CO's 2-3xBB raises with fair frequency.
We're dealt AQo in the small blind.
UTG folds.
CO is all-in for 4BB
Button folds.
We...call? (I did.)
BB now raises all-in over the top.
Now what? I called this too.
Which plays on my part were mistakes here?
What is you minimum holding to choose my actions (call and call)?