Okay, wow; I didn't know people were out there writing completely inexcusable grammatical errors. I would take a wild guess about the scar business and say that some people probably thought it wasn't a real scar at any point, that it never bled and then stopped bleeding, but just started as a mark, like from a brand, and Harry just grew up assuming that it was a scar from some piece of metal hitting him in the forehead and then he was just used to calling it a scar. The film shows the cut as hair-thin, so it's sort of believable it would have healed in just a few hours.