If it indeed is a scratch, sometimes it is hard to tell if it is really a scratch or if the line was in fact caused by the nozzle oozing onto the top surface during the move. Time to get out the magnifying glass to check.
Signs there’s scratches on the top layers:
There is a visible scratch on the top layer that is not a line from oozing filament.
Explanation:
The long scratch visible on the top layer in the picture shown was caused by the nozzle dragging across the top layer when moving across to go on printing the rest of the frame around it. Most likely, the 3D printing surface of that layer is over-extruded (or slightly warped or pillowed) and that’s why the nozzle scratched it in the move.
How to fix:
One approach would be to try and fix the over-extrusion or the warp. See [Over Extrusion] and/or [Warping].
Another is to use the Z-Hop feature of your slicer. Z-Hop will lift the nozzle up a certain amount before moving across to prevent the scratch.
Use combing (also known as “avoid crossing outline”). With combing, the nozzle will travel along the outline instead of crossing it and going straight across your print, which will often avoid this issue entirely (though not necessarily in this example).