You're accent is inherently a part of who you are, but it doesn't make you any less Nigerian to speak with a non-Nigerian accent, and speaking with an American accent, despite having no connection with it doesn't really make you American. If you like, an accent is more of a symptom than an cause. You can tell a lot from it, but in no way does it actually define who you are.
I'm from the South, and I'm always getting told of from my friends up North (where I live now) for speaking live a chav just because of little things like saying 'thirst' like 'first' and 'thirteen' like 'firtean'. None of that really matters, but there are certain associations with particular accents and dialects, thankfully pretty much everyone on the plant knows these assumptions are bull**** and don't think twice about accents.