[MikeSid]

Raise or lower the fixture height.
If the wires come from below, lower the fixture height to allow enough line to center the fixture.
If wires come from above, raise the fixture height.

This will require that you get into the wall and probably remove a staple that holds the wire to the stud. But it doesn't look like need to move it too far to center it, and you might have enough line if you change the fixture height.

It's a compromise and will require a bit of drywall work. But it beats fishing a new line.