Help with a neck plug gap please?

[Kitkumi]

I just finished up a custom that I have been working on for months off and on and she came out PERFECT.... right up until I moved her head!

I replaced the head and neck plug so that her head can still turn. I had a little bit of trouble getting the plug back in the head but by the end of it everything looked good, I tested it with the body and it worked and looked good so I glued everything back together and let her set. Now, however (it has been a few hours) there is a little bit of a gap between the head and the neck and when I turn her head it becomes a pretty big gap.

Everything looks like it is on straight so I'm not sure where this problem has come from. Does any one have any advice to fix it? (I'll probably find a nice ribbon to tie around her neck if it can't be fixed). Thanks