2 yr old with hard lump on top left side of head

My 2 almost 3 yr old daughter has had a small hard lump on the upper left side of her head near the hairline for at least a year. I think it has changed a little, flattened a bit and perhaps widened a bit. It sort of feels now like it has a double ridge at the top. It's a little less than a quarter of an inch wide and, while it can be seen if you look very closely, it is not discolored in any way and she says it does not hurt. She does not seem to have any other symptoms of anything, though once or twice she has complained of her tummy hurting lately, it's always been at bedtime when she was trying to talk me into staying in bed with her, so her motives are suspect. I took her to the pediatrician when I found it last year and he said it was a calcium deposit, probably from an injury, and that it would go away in about six months or so most likely. I could not recall an injury to that area, but while she was not an infant who banged her head exactly, she was nearly so. She liked to sleep with her head up hard against the wall as a baby and had a tendency to bang her head into things fairly often. The size of the lump has not changed significantly, but does seem a bit wider and flatter to me, as I said. I feel quite stupid for not having taken her for a second opinion. She seems healthy. If it were cancer, would it go for longer than a year without some other symptom?