It is intruding into the chamber where the plug is.
It is not on the plug.
Its so close to the plug that the socket can't get past it.

It is coming out from around the tube.
It is intruding into the chamber where the plug is.
No it is not on the plug

The spark plug tube should be pressed into the head and have no gasket.

As Patonium, states check for any remains from the spark plug boot.

Make a hook from solid steel wire and try to pull the gasket out.