If you get the Gospel wrong, and preach it to others, you are a False Teacher.
Everyone has faults and mistakes and misunderstandings and things they are growing in in their teaching.
Being wrong about many things does not make a person a False Teacher.
False Teachers prevent the eternal salvation of others through their false teaching, by teaching a False Gospel.
Paul the apostle damns False Teachers to Hell, twice, in Galatians chapter one.
The only true Gospel is found in 1st Corinthians 15:1-4.