Answer
Rinse and dry the surface before sanding more. Some marks are dried slurry, not scratches.
Why it happens
Dirty water, dried slurry, or uneven wiping can leave marks that look like sanding defects.
Recommended grit
Continue with the current fine grit only after cleaning and inspection.
Wet or dry
Wet.
Success check
The surface looks even after it is rinsed and dried.
What to do
- Rinse the surface with clean water.
- Wipe slurry before it dries.
- Inspect the dry surface under good light.
- Resume sanding only if actual scratches remain.
Avoid: Do not keep sanding a stain that is only dried slurry.