This is an old episode of some sci-fi series: humans are fighting aliens in space, and at the end of the battle only one human remains in a spaceship going to the main planet of the aliens. At the end he drops a bomb to destroy the alien planet and realizes too late that the aliens sent him back to Earth instead of their planet.
Does it ring a bell to someone?
This is following episode of "The Outer Limit" series:
S. 2.E. 18 The Light Brigade
This is the outer limits episode The Light Brigade featuring Wil Wheaton.
The ship is on a mission to destroy the aliens' home planet, however some of the crew are secretly members of the alien race. After a series of revelations, betrayals and counter-betryals Wil manages to reach the firing controls and drop the bomb.
He then opens the window to find himself looking at Earth.
