Ultimate Compound is absolutely worth trying, and follow up with Ultimate Polish.
Looking at your image. There are lines that appear to be in arcs.
Thinking these could be your sanding marks? If so, Ultimate Compound may remove them. Then follow up with Ultimate Polish.
Or they could have been inflicted by contaminants getting into the polishing pad. If it is these, you may be able to clean the area again and use a fresh clean pad with Ultimate Polish.