@talk72000,
Maybe most people as you say consider Finland to be Scandinavian in common English usage,and also, Iceland, the Faroe Islands and Greenland are sometimes erroneously considered part of Scandinavia
Scandinavia is a region in northern Europe that includes Denmark and two of the Scandinavian Peninsula's nations, Norway and Sweden.
Swedish and Finnish are both accepted languages in Finland. But to say the Finns speak both Swedish and Finnish is not correct. There are many who do not speak Swedish as Swedish has not always been taught in the schools. I know a couple of Finnish ladies who do not speak Finnish.
Then there used to be Swedes who never spoke a word of Finnish, but they can now learn it in school.
5% of the Finns have Swedish as their mother tounge.