The Annex was the target.
The attack on the “consulate” was a diversion, and the death of Stevens was an accident.
Could be. Or, the attack on the Consulate was designed to lead the attackers (following the escaping Americans from the Consulate) back to the (supposedly secret location) Annex.
Note that the attackers did not hit the Annex quickly after they hit the Consulate: It took them until after all the Americans had reached the Annex to begin the attack on the Annex.