as others posted, the gap is no problem, usually;
But if you want to fix it, its actually pretty simple;
Remember though, this is still electricity, and can kill you instantly.

The general procedure of fixing would be:

• Turn off electricity in this room. Check (using a device which certainly works) it is off. Make sure no one can turn the electricity on again.
• Unscrew the screw in the center piece, take off the center piece (and the outer frame)
• There are probably little claw-like things that connect the plastic-/metal-device with the wall. Loosen them, place device farther inside the hole (care to not displace the cables too much), tighten them against the wall again
• put on the frame and the center piece, screw in the screw
• turn on electricity, check if everything still works

If youre experienced, this whole process might be done in, i dont know, 2 minutes?
Unexperienced, half an hour is okay too ^^
Just dont kill yourself ;)