No, one bomb is not enough, unless you're terminally paranoid and exaggerating. A Cold War Russian 'small penis' bomb, yes, but realistically, no-one uses such large weapons anymore, and certainly not Iran, if they even have the tech to make a nuclear weapon.
Desire and actions are two different things. Iran knows that attacking Israel would be a stupid thing to do, and realistically out of the two Israel is far more likely to be the aggressor in this situation. Hell, they already asked the USA to give them some bunker-busting bombs so they could strike Iranian facilities.