Sanding the top deck edge..

In a case like this I would make a miniature sanding block and use 400-600 grit sandpaper to remove the putty. I take a small piece of wood about 2.5" long by .5" wide, cut a strip of aforementioned sandpaper about 3" long, and superglue it to the block. In the situation you describe, I would wet sand the deck where the putty is as carefully as I could using the sanding block in a fore/aft motion rather than port/starboard to avoid rounding the edge of the deck where it meets the hull. Should you have any putty on the hull itself, use another small piece of sandpaper and with a fore/aft motion to wet sand it off with your fingers. You may have to use finer grits to remove any scratches caused by the 400-600 grit sandpaper.
Hope this helps. Good luck.
Dick McC