We sin when we take the elements of the Lord Supper with sin in our lives. It is our attitude that condemns us, the elements do not save or cleanse us.
Confession is Biblical but not as confession is practiced in the Catholic Church.
1 John 1:5-10
5 And this is the message we have heard from Him and announce to you, that God is light, and in Him there is no darkness at all. 6 If we say that we have fellowship with Him and yet walk in the darkness, we lie and do not practice the truth; 7 but if we walk in the light as He Himself is in the light, we have fellowship with one another, and the blood of Jesus His Son cleanses us from all sin. 8 If we say that we have no sin, we are deceiving ourselves, and the truth is not in us. 9 If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. 10 If we say that we have not sinned, we make Him a liar, and His word is not in us. NAS
Have you read 1 Peter?
1 Peter 2:9-10
9 But you are a chosen race, a royal priesthood, a holy nation, a people for God's own possession, that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light; 10 for you once were not a people, but now you are the people of God; you had not received mercy, but now you have received mercy. NAS
We are all priests and are a royal priesthood, we confess our sins to God not to a priest and God forgives.
As to what you posted from John 20 you posted only a portion of what John wrote:
John 20:19-23
19 When therefore it was evening, on that day, the first day of the week, and when the doors were shut where the disciples were, for fear of the Jews, Jesus came and stood in their midst, and said to them, "Peace be with you." 20 And when He had said this, He showed them both His hands and His side. The disciples therefore rejoiced when they saw the Lord. 21 Jesus therefore said to them again, "Peace be with you; as the Father has sent Me, I also send you." 22 And when He had said this, He breathed on them, and said to them, "Receive the Holy Spirit. 23 "If you forgive the sins of any, their sins have been forgiven them; if you retain the sins of any, they have been retained." NAS
At the time Jesus was crucified the disciples number about 120.
Why is the Catholic Church off base? Where should I start? Images, transubstantiation, baptismal regeneration, works increases justification, the Papacy, praying to the physically dead, Mary is the mother of God, the list is long.
If anyone needs to be shown the light it is those who live in the darkness of religion and not in the light of the Lord who set us free from religion.