Cosmology Principle vs the actual center of the Universe

Because the 'location' where it occurred is 'everywhere'.

No - it is a reasonable representation. Arbitrarily pick any spatial coordinate on the right hand side of the diagram as of 'special interest'. Now move to the left, (keeping the same spatial coordinates but going backwards in time). Eventually you'll arrive at the big bang. Now pick another spot and do the same.Now look at the big bang. Point to a single spatial coordinate that exists that is not at the big bang at the time of the big bang.You can't.Why? Because the big bang happened every'where'. Confused? That's a good sign. Here's another diagram If it still doesn't make sense - keep reading about it. It's difficult to think in four dimensions so 'pretend' the universe has only two spatial dimensions and one temporal one - you'll pick up the 'gist' of it in I'm sure.