Very, very unlikely. Iran is not going to start WW3, however, it could have a massive short to medium term rippling effect across the region and on the price of oil, thus raising prices across the board. This obviously is not good, even if it does not mean WW3.
But by what happen for now, this was an attempt for the world war. By the world, we can't say on what the Iran plan and goals because everything would affect by that specially on the resources they bring to us so how was it? What if they do much more?