When you select the dark background, use the same (multiple) area(s) as you selected for Background Neutralisation. No need to do twice the work.
And tou really only have to select the biggest and brightest galaxy as the target for your Colour Correction.
Don't try and 'double-guess' what PI might be doing - just select multiple ares (as needed) at the core of your galaxy, PI knows what 'is not data'.
Use the ability of PI to aggregate multiple preview into a simgle preview or image file.
Hope this helps.
