[AUCTeX] Problem with wrapping

[Frederic]

Hello!

I have finally installed Linux and after a bit of trouble, Emacs is working 
fine!
I am very happy with it, because it integrates well with xpdf, so that I don't
have to close the pdf before I compile with pdftex.
Anyhow, on to my problem. I would like to add an auto-wrap feature in addition
to a justification feature. So, here is the code I have in my .emacs file :

(add-hook 'text-mode-hook 'turn-on-auto-fill)

(defun auto-fill-hook ()

(auto-fill-mode 1)
(setq default-justification 'full)

(setq fill-column 120))

However, I used to have it set at "80", but I don't see the difference with
"120. The auto-wrapping at the 80th column is not to my liking since I have a
small laptop with a 1360x76 resolution, and I would like to extend the range of
the auto-wrap.
Additionaly, it seems that the justification is not working.

Hence, I am wondering what is wrong with my code.

Thanks for the help :-)