Don't feel too bad, it's a really difficult test.

As Bruyere noted, those bits are on the subtle side.
On the other hand, it does seem to me that with all of the traveling and relocating people are doing nowadays, accents
are becoming less pronounced here. Maybe not much, but to my ear I hear a lot more variety. Where I live, there are so many different accents and dialects, both home-grown and imported, that it'd be difficult to tell which is the 'regional' one, I think.
I grew up with a rather pronounced Wisconsin accent (no, it doesn't sound like the one from Minnesota

), but having lived in California for many years, it's largely disappeared, unless I'm very tired. I can turn it on and off at will easily, though. I've met many people like that; I think in another couple hundred years or so there could very well be one generic "American" accent of sorts.