If I cannot play additional cost to play something like sacrifice, my card go to hand again?

Yes — if you can't pay the additional cost, the play is cancelled and Sacrifice returns to your hand.

When you start playing a card it moves from hand to the Chain, but you have to pay all costs in step 4 of the play process (killing a friendly Mighty unit here, Rule 357.2). If you can't or won't pay it, the legality check fails and "the actions taken in this process are undone and the action is cancelled" (Rule 358.5) — so the card goes back to hand, no costs are paid, and nothing from the card happens.

Note: Sacrifice's cost is mandatory — if you have no friendly Mighty unit to kill, you simply cannot play it at all. You also can't pay partway and get a partial effect; it's all-or-nothing.