Plan B or implantation???

My boyfriend came in me June 27 and then some family issues happened that we completely forgot about taking Plan B. I ended up taking it 4 days later…. I read that I might be less effective after 3 days which makes me kinda nervous. I started light spotting for 1 day, 5-6 after I took the pill. At first I thought it was Plan B spotting but then I become aware that it could also be implantation bleeding if I took the pill too late and it didn’t work.

Could it be Plan B spotting or implantation bleeding??