Missed AK on a coordinated flop

[MrOnizuka]

UB 20+2

4 people left at the 75-150 blinds level. Me and the SB have around 3K, button about 2K, and BB is big stack with around 7K.

I get AKo utg and raise it to 455. Button folds and the SB calls, BB folds. Pot is 1060.

Flop comes 7 8 9 with two diamonds, of which I possess none. SB checks to me. No real read, but he hasn't done anything crazy, got most of his chips winning a flip against the 5th place guy.

What's my action?