Here's how I do full screen. My windows are fixed size so you'll probably want to restore the window size as well.

gistfile1.m

-(IBAction)toggleFullScreen:(id)sender
{
    NSWindow* myWindow = self.window;

    self.fullScreen = !self.fullScreen;

    if (self.fullScreen) {
        _normalWindowMask = [myWindow styleMask];
        _normalWindowLevel = [myWindow level];
        NSRect mainDisplayRect = [[NSScreen mainScreen] frame];

        [myWindow setStyleMask: NSBorderlessWindowMask];
        [myWindow setLevel: NSMainMenuWindowLevel + 1];
        [myWindow setFrame: mainDisplayRect display: YES animate: NO];

        [myWindow setOpaque: YES];
    } else {
        [myWindow setStyleMask: _normalWindowMask];
        [myWindow setLevel: _normalWindowLevel];
    }
}