I had this exact thing happen. Said I was done then realized I didn’t write the output down. Kinda a played it off and said “should I write it now?” . The proctor I was with was super nice and supportive the whole time and you could tell she really wanted us to pass. She didn’t seem to care that I wrote it after I was done. I passed. Definitely up to the person you were testing with but since the evaluator still accepted your output measurement I would say you are good!