I accidently closed the "align and distribute objects" pane, which I had docked on the right-hand side of the screen along with a couple of other tools. I have reopened it using the toolbar icon but it's just free floating rather than docked, and no matter how I move it around, try to arrange it etc, it just won't dock back to it's original "locked" position and just remains a floating window. How do I get it to dock in the same place / arrangement as it was originally??? Thanks! :)

Try this. Grab the panel by its title and wait for the blue indicators left and right and when the "+" sign appears release: