If you were to say 'Money is God' then must I deny the existence of money?
I believe the ultimate truth is something like an ultra-fundamental physical law, something from which the laws of thermodynamics, quantum physics and space time all derive. It is usually called a 'theory of everything'.
Why it is not a god is that it has no mind,just as the 2nd law of thermodynamics has no mind.
God - it is said - so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life."
A 'theory of everything', a law of physics does not love, nor beget sons nor grant eternal life to those who believe in it - it only defines the charge on an electron and the strength of gravity. Everything else is a consquence, a playing out of what follows from that rule.
If you want you can call such a ToE my 'god' and say I am a believer - I can't stop you doing that, but I'll still call myself an atheist.