Centre of the singularity that is the big bang
Since the Universe evolved from something like a singularity, where all of space was contracted to a point, yes, we are at the center of the Big Bang. So is every other point in the universe.

The CMB represents the light from a universe-filling plasma that lasted for roughly 378,000 years. It is a feature of the observable universe, rather than something that is actually there in the present universe; in particular, we can never reach it, as it's the same distance away from every point in the universe. As such, there's not much sense in talking about what's behind it, much like talking about what's behind a shadow.