I'm not a creationist either, but I do believe that anybody, who asks questions about the origin of the universe, tells the same old story in modern verse, so that it is poetry at best and not science.
By asking, why it is assumed that the universe has no centre, you expect an answer from science. But science cannot enlighten you about its own assumptions, it can only provide consequences from these assumptions.
In my previous post the meaning of the word "locate" must have surely mislead you, just like the word "birth"...that is why I hold that any analogy expressed in common language is actually misleading here.
You claim that there must be the centre. So you can think of the possibility of a centre (that is what I meant by "locate"). But then you take pieces of scientific arguments and try to argue for the converse assumption analytically, on purely logical grounds, i.e. you try to generate a contradiction. For example here:
But purely logical analysis of scientific arguments produces tautologies, because any scientific inquiry needs premises that evolve on reasonable grounds, not by logic. Otherwise you get rationalism, that leads once again to metaphysics.
You cannot argue for the assumption "there must be a centre" by using the evidence of the theories, which are based on the converse assumption. All that is left is the obligation to derive a consistent theory from your own premise. This is the only way to prove the validity of the converse assumption. And I bet that will be a task too tough to cope with!