Rosie - after living here for many years, I've come to the conclusion that it really ought to be 'I'm a native American English speaker' since there have been so many other cultures impacts on how things are spelled and pronounced - and even British English in going through the same morphing right now.........
I often laugh when people from various states 'help' me with pronunciation of English words - because it's all based on their (often limited) understanding! I was even threatened by a person (who was of German decent) that I should learn to speak 'properly'.........

:mg: