The Catholic Church is not a denomination. Protestants have denominations.
I checked the definition before I posted to be sure I was using correct terminology. If you believe that no one can be a Christian unless they belong to the Roman Catholic Church, then I can understand why you don’t recognize what you consider the only way to believe in God is a denomination. Nevertheless, it is. And all who are saved through the blood of Jesus belong to the catholic Church but not necessarily to the organized religion known as the Catholic Church.
You're right, the organization under the Bishop of Rome is more like a sect, than a Christian denomination.