I don't know what abnormally large head is but was embarassed to admit it. Can someone tell me?

Head size varies. There is a wide range of normal head size from ~18-24 inch circumferance in adult & by itself means nothing more than being very tall or short.One or both parents of an identified kid will often have a lg head size.In some kids increasing head size could represent an abnormal accumulation of fluid in the brain.
More room for brain! There is nothing wrong with having a large head. Macrocephaly is just a descriptive term, not a diagnosis. Some very successful and famous people have it. Keep yourself an equally large smile!