No, it is not making stuff up. We simply make the following argument.Asserting that science proves or points to the universe not being created is making stuff up. Assuming/believing the existence of the universe is a fluke is totally different story.
1. We should believe worldviews that makes predictions that is more consistent with observation of our empirical reality.
2. Worldview X is more consistent with observation of our empirical reality than worldview Y.
3. Thus, we should believe worldview X.