Don’t worry. We have the entire gospel. A church describing itself as Full Gospel is probably Pentecostal.
The emergence of Pentecostalism at the turn of the century saw the rise of groups claiming to restore the Christian church to its primitive fervor by a renewal of the charismatic (Pentecostal) gifts mentioned in the Bible (Acts 2:3-13; 1 Cor 12:8-11). These gifts include speaking in tongues; interpretation of tongues; prophecy; gifts of healing, knowledge, and wisdom; and miracles.
Pentecostals regarded these gifts as signs of the Holy Spirit’s work in the last days, so churches which lacked them were viewed as deficient at best and apostate at worst. Christian bodies which accepted Pentecostal gifts, whether denominational entities or independent local churches, were considered to possess the fullness of biblical revelation, hence the name Full Gospel.