Yeah, nah, that's not how Christianity works, or how religions work outside of tiny movements or strict organisations.

Almost from Jesus's death Christianity diverged as the gospel spread through word of mouth, it's why alongside the canonical Gospels you had various different non canonical Gospels, because before things were written down and a canon formed, people told different stories about Jesus.

You also had various different Christianities form straight from the getgo. The Thomasines, the Coptic Church, the Ethiopian church are major examples, The Gnostics are a more extreme example. Hell in the bible itself you see two different currents with Paul and James.

Also the idea that one follows the "One True Church" is a silly statement if you glance at the Bible or records of the early church. Do you attend a house church, where members of the community worship at someone's home? Do you take communion as part of a symposium-like meal like the early Christians did in Paul's time? Do you reject traditional property norms, holding things in common? Do you, as Jesus said before telling us the Lord's prayer, reject big public shows of piety and long babbling prayers, only saying the Lord's prayer?

As religions spread, they begin to develop variations, with Protestantism doubly so. Saying Catholicism isn't a form of Christianity is akin to a Theravada Buddhist saying that they are the only true form of the Drama, or an Anarchist saying a Trade Unionist isn't a leftist.