I am trying to move my light fixture in my bathroom over about a foot to the center of the wall. After removing the fixture and taking the junction box out, I can see that the wire is not long enough to move over.What are my options without having to call in an electrician?

You cannot wire nut an extension and hide in the wall, that is not code. If you have access in an attic, pull the old wire to a junction box there and run a new lead to the new position. OR, pull a new longer lead from the wall switch. Only other way is to use the old jbox and an extension from there but the old box must be accessible, behind a mirror perhaps.