Nobody born in the USA is 100% (insert other country here)
Your 100% American but of (insert country) decent
If you go back to as my grandparents used to say "the old country". Say Ireland, Or Italy for example. You wont be viewed by the inhabitants as Irish or Itallian. But as an American.
Me, I'm of mixed decent.
German,Irish,English,Spanish,Hungarian,Slovak, and Prussian.