03-09-2019, 06:26 PM
By default the Ellipse select has anti-aliasing so border pixels are partially selected, and so partially painted.
Either redo the selection after un-ticking the Antialiasing option in the Tool options, or use Select>Sharpen on your current selection.
Either redo the selection after un-ticking the Antialiasing option in the Tool options, or use Select>Sharpen on your current selection.