NK
The “fullness of the faith” is always Christ.
Things added over thousands of years - including paganism - is a pollution of Christ’s sacrifice. It can never save.
And of course, maybe you thought you were saved, but never came to faith...
The fullness of the faith is found in the Catholic Church, specifically the seven sacraments, instituted by Jesus Christ, with the Eucharist being the most important. The Eucharist, practiced by real Christians the world over, for 2,000 years, belittled by heretics for the last 500 years.