People keep saying we are a "center right" nation, and yet polls consistently show voters support Democrats on nearly every issue. So I don't see the evidence for this claim, unless you believe the Democrats are the centrist party and the Republicans the far right party, in which narrow preferences for Democrats would actually be considered right of center.
I would agree that we are a center-right nation compared to the rest of the world, but certainly not in a context in which Democrats are considered left and Republicans right.
The whole notion of there being such a thing as a "center right" or "center left" nation is kind of nonsensical, since there's no widely agreed upon definition of where the political center is. You can come up with some kind of scale relative to other countries, I suppose, but it's pretty much impossible to plot all the countries of the world on the same ideological spectrum, since the issues are so different from place to place.
Or you could just define the ideological center in the US as being the ideology of the media voter there. If that was your approach, then the US is "centrist", by definition.