How to reinstall Gala

So, I've been tweaking my elementary and after installing gnome-tweak-tool I'm not able to run Gala.

After a restart, the windows were without title bar (no close button etc.). So I ran Compiz (compiz --replace), and it's working. But it has several issues (like the title bar entering below the Elementary topbar and the Elementary keyboard and mouse shortcuts does not work on Compiz)... and it's too slow to open (I had to put it in Session applications).

From Compiz, when I try to run Gala (gala --replace), I have, in the terminal:

jefs@JefsPC:~$ gala --replace

(gala:14241): Gtk-WARNING **: Theme parsing error: gtk-widgets.css:756:1: Expected semicolon

(gala:14241): Gtk-WARNING **: Theme parsing error: gtk-widgets.css:776:0: Expected a valid selector

(gala:14241): Gtk-WARNING **: Theme parsing error: button.css:150:14: Not using units is deprecated. Assuming 'px'.

(gala:14241): Gtk-WARNING **: Theme parsing error: button.css:150:14: Junk at end of value

(gala:14241): Gtk-WARNING **: Theme parsing error: granite-widgets.css:144:14: Not using units is deprecated. Assuming 'px'.

(gala:14241): Gtk-WARNING **: Theme parsing error: granite-widgets.css:144:16: Not using units is deprecated. Assuming 'px'.

(gala:14241): Gtk-WARNING **: Theme parsing error: granite-widgets.css:144:22: Not using units is deprecated. Assuming 'px'.

(gala:14241): Gtk-WARNING **: Theme parsing error: toolbar.css:110:13: Not using units is deprecated. Assuming 'px'.

(gala:14241): Gtk-WARNING **: Theme parsing error: toolbar.css:110:13: Junk at end of value

(gala:14241): GLib-GIO-ERROR **: Settings schema 'org.gnome.mutter' does not contain a key named 'center-new-windows'
Trace/breakpoint trap
jefs@JefsPC:~$

Will reinstalling Gala solve this? Is there some way to 'reset' it? Or I can create the key "center-new-windows" on org.gnome.mutter (I could not create a new key using dconf)? What can I do to have it back?