"For where two or three are gathered together in my name, there am I in the midst of them." Matt 18:20
Amadeus, you aren't incorrect, because no matter where you are, Christ is right there with you if you've received Him, but in context, Matthew 18:20 is about discipline in the church and correcting sin.
18 “Assuredly, I say to you, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven. Matthew 18:18
This might not be entirely clear just from Matthew chapter 18, but Jesus was a rabbi and taught from the law of Moses and the prophets. It's very important to understand that the law required 2 or 3 witnesses to establish testimony in any legal matter, and everything Jesus did was in fulfillment of the law.
“One witness shall not rise against a man concerning any iniquity or any sin that he commits; by the mouth of two or three witnesses the matter shall be established. Deuteronomy 19:15
This principle is repeated in the law, by Jesus Himself, and then again by the Apostle Paul in 2 Corinthians 13:1 and 1 Timothy 5:19.
Even when concerning the testimony of our Lord the same principle is applied:
6 This is He who came by water and blood—Jesus Christ; not only by water, but by water and blood. And it is the Spirit who bears witness, because the Spirit is truth. 7 For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one. 1 John 5:6-7
This is also critical in putting the last of the Lord's enemies under His feet, those hosts of spiritual wickedness in the heavenly places, because their conviction can only be by the faithful and true testimony of 2 or 3 witnesses, not just one.