keep American accent British?

Dont accents just have a natural tendency to change when in a new environment [...]
No, it actually works the other way around -- language change is quicker in the longer-settled regions, newly settled ones are generally more conservative.
 
You mentioned that you live in southeastern Michigan, which might explain it. Depend on exactly where you live, you may be on a peripheral area between the "General American" accent and the full "Upper City Shift" accent. Some more maps from the website I had linked to:

I just listened to that youtube video you linked, and I agree with funnyhat. I'm from southwest Michigan, the Kalamazoo area, supposedly the very heart of the NCVS region, and I also thought the samples of that woman talking, where she pronounces "busses" like "bosses," sounded very strange, and not at all like how people around here talk. I should have listened to it earlier in the thread, cause funnyhat's right.
 
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