you could be beat. but he could have also been trying to get AK to a showdown as cheap as possible.. or been slow playing a lower set not realizing you spiked a set also.

he probably doesnt think you raised UTG w/ 88, so hes using that A against you, hoping you hit it. with that knowledge he probably has a straight or a lower set.. possibly flopped a small flush and with no 4flush coming he knows its good.

but im probably calling here.. its too big a hand to fold to a 3 bet on the river.. especially when the A comes.