I will tell you what happened.
when you are looking for something that isn’t there, but you want to find it, eventually you will start imagining it. I would suggest taking a break from staring at the coin, and look at it again in a few days. That is if you genuinely believe that it’s a “3”. Because it’s not. I had something similar happen to me, when I was going through my “1947 Canadian nickel” looking for a dot variant. I would spend nearly an hour looking at one coin, at various magnifications(even 200x) trying to find a dot, that wasn’t there. I realized that I’m just being delusional, took a break and looked at my coins again in a couple of days. Sure enough, nothing was there.
sometimes the excitement of an idea that, maybe, this is that rare coin, derails logic.