Where did the universe come from? Atheistic origin science has no answer.

[Angrboda]

he calculated the energy of the whole universe and got exactly 0.

So if the energy of the universe is not exactly 0, the Big Bang is false then. Else why bring it up.

But he could not have calculated the energy of the universe, since not all of the universe is even observable.

Besides all observations show the universe does have a mass-energy that is not 0, so the Big Bang is falsified until we get an exact 0.

No, if the total energy of the universe is non-zero, then it counts as evidence against his theory, nothing more. The big bang is a separate theory, explaining a different phenomena. At present, it's not entirely clear whether the sum total is zero, but there is substantial evidence that it is zero or close to zero. That makes his theory potentially correct. However, as there are other theories that accord with the evidence, as well as theories as yet unknown, it doesn't make his theory necessarily true, nor does it make his theory a conclusion based on an assumption of atheism, or to atheism.