first of all, why you raise to 3.5xBB ? I prefer raising smaller, like 2.5xBB or at most 3xBB. You will save chips anytime you have to fold to a raise or if you want to give up your hand on the flop.
Then I think it depends a lot on your opponent, if you should call AK here or not.
And you have to take a look at the odds
, of course..
lets say stacks are both 20BB .. You raise to 3.5 (= 5BB in the pot [Raise+SB+BB]) and the BB shoves for 19BB more (plus his BB its 20).
Now there are 24BB in the pot and you have to put in 16.5BB more ..
You dont even get 2:1 so you shouldnt search for a flip here.. And if you think your AK will flip against that opponent its an obvious fold imo!
Just look for a better opportunity to get your chips into the middle imo.
16.5BB is still a playable stack (and if you only raised to 2.5BB you could have 17.5BB here )