You are correct, a creator cannot exist forever. That is not, however, how Catholics view a Creator. Catholics view a creator as extra-temporal. You may think that these are the same thing, but Physics actually supports the pre-existence of an immaterial thing with regard to time. It relies upon Einstein’s theory of Special Relativity and quantum theory.
It was theorized by Einstein that while time is the forth dimension of space, it is also affected by gravity. High concentrations of gravity actually slow time down. This has been proven. Time has been observed as going faster in orbit on the ISS and requires regular clock synchronization.
If you are correct and the universe does have a starting point (which I agree with you on) and expanded in the big bang theory, then the further back in time you go and the closer you approach the big bang, the stronger the gravity. The stronger the gravity, the slower the time. Time slows to a halt at the initiation of the Big Bang. I am not even speaking of the instant before the Big Bang.
I’m speaking of the Planck epoch, everything before the first 10^-46 of a second of the universe. The so called “time” of the Planck epoch is theoretical as there was neither space, gravity nor any quantum particle for time to be dependent upon. 10^-46 seconds simply denotes a quantum change. It is only after this quantum movement acted upon already-existing energy that the universe expanded and time sprang forward.
Physics already orders the the causality of events within the Big Bang which precede chronology. Why can we not speak of Creator which also causally precedes the quantum change that started it all. Your argument from contingency states that that quantum movement must be contingent on something else. There is nothing else present which can cause the change as the only thing which existed was pure, dense and unmoving energy. We call that illusive cause which caused the quantum shift and set space, time, and the quantum forces accelerating outward our Creator.