Why cannot see any link to your blend file in your post ??
I have tried to upload the file but it wont let me upload for some weird reason
Cancel creating this face, switch off visibility for Mirror modifier or switch off triangle icon on modifier which allows to modify both sides.
Better yet separate all what belongs to head into it’s own object (select, P to separate); when you finish head you’ll be able to join back objects.
In edit mode select 2 lower neck shape vertices, cursor to selected, and in Object mode make sure Origin is where cursor is.
In front view edit mode make sure middle loop is scaled 0 on X axis.
If there still are problems post blend with head only (delete body, Save As) on pasteall.org/blend, copy link from address line here.
Usually when something like this happens, the vertices are set up in a way that causes the creation of a concave face or a bowtie face (because the fill tool will make use of every vertex in the selection).
I found out that the mesh model was being on the right side, and the frame was being on the left side… How ever there was a problem when i tried to move them out to their original position so here you go
Make all mesh mirror on one side - scale loop vertices X-1 or Ctrl-M on x and it flip to the right side. If you switch off visibility for a Mirror mod - all on the right.
http://www.pasteall.org/blend/37857
It’s more convenient to model bigger scale and then adjust to some units. I find it easier that way.
yeah definitively a misstake by me, thanks a lot for the help ^^