We scraped off the popcorn. Filled the imperfections with joint compound and sanded the areas. We added joint compound to the paint in an effort to smooth the rough scraped areas and blend with the smooth areas. The differences are still very obvious. Any suggestions on how to even it out?
WHooa… bad attempt… now all you can do is use a Texture Paint, applied with a special Texture Roller… you unfortunately cannot get a "smooth" surface starting from where you are, short of having a Drywall Contractor ReGlaze the entire ceiling with new plaster… then (if you choose that route) wait 2 weeks for the new plaster to cure, then prime it with a Pigmented Shellac Sealer Primer… then finish coat with a high grade Acrylic Paint (a flat finish looks best on ceilings) Good Luck!
Either a full skim coat with drywall mud, entire ceiling, as mentioned or add a different texture. <a href="https://www.house-painting-info.com/apply-orange-peel-drywall-texture.html">Orange peel texture</a> or a <a href="https://www.house-painting-info.com/apply-drywall-brush-texture.html">brush texture</a> are fairly easy to apply.