When your fingers almost can't feel the lump any more, quit scraping. Grab some wet 600 grit paper and wrap it around a small hard block. This one is balsa. Hard rubber blocks work nice too. Foam blocks are too soft for this task.
Using light pressure skim the surface over the run. The idea is to cut the remaining high spots without skinning the surface around them. It will only take a few strokes to flatten the surface:
Now switch to some wet 1500 grit, which you can hold freehand. Make a few more passes. Your goal isn't to remove any significant material. You just want to remove the 600 grit scratches. After that you can go straight to compound. It can wait until later when you're running the buffer, but for this example I just hand rubbed it a few minutes. Run all gone:
Ok ants, let's get some work done....