Sorry, but it is true that the Catholic church was the first Christian denomination.
The truth of this statement depends quite a bit on what you mean by "the Catholic Church."
Yes, the current Catholic Church can trace its lineage back very early, but it's not like that early church would have had much similarity to the modern Catholic Church.
I mean, we're talking a few centuries before the Council of Nicea, so it's questionable how much those early Christians would have agreed with the Nicene Creed if they had known about it.
I think it's debatable how much any of them were even trinitarian.