Remember, in 1948/1949 50 cents was relatively a lot of money
My feeling is that you purchased your stamp before the real value was known. Even in the late forties, it should have been more than 50c.
But a small crease may have had something to do with it.
Still, it has a personal historical fascination and that makes it a treasure.
It is also a very beautiful stamp...indeed, the whole set is lovely.
Look after it.