Baby soft spot help

How soft is a babies soft spot? My two year-old through a ruler and it hit my three month old on the top of the head, he didn’t cry he seems totally fine I could never really find his soft spot I know the doctor says that it’s there but for some reason I can’t feel it so I don’t know what to look for if there is anything to look for I’m super anxious and paranoid about it I tried to make sure his head is protected at all times and now I just feel awful.