Try again. Fort Sumter had already been fired on by the rebels when Lincoln ordered the blockade. So the war had already been started by the enemy.
You are wrong on two levels. First, the United States Congress stated that the official opening of the war was the declaration of the blockade, and not the Charleston defense of its harbor.
If you still want to hang on the first to fire rationale, I will point out to you that it was Union Lieutenant Daniel Tompkins who fired the first shot in Charleston Harbor.