To understand the scripture in question one must understand the background into which it is introduced.
The Jews were taught that God made provision to cover their sins through a vicarious sacrifice. In the temple the high priest sacrificed a lamb for the sins of the people. The sins of the people were deemed to be placed upon the innocent lamb and through the shedding of the lambs blood the penalty for sin was paid.
This is the imputation of sin and righteous that we see in 2 Cor 5:21. God is imputing our sin to Christ and Christ's righteousness to us. Christ was not guilty of our sin and we do not merit the righteousness of Christ.
Vicarious atonement is a well established principal in scripture and Jewish history. Sin requires the death penalty which Jesus took in our place. Jesus took our sin upon Himself that we might receive His righteousness.
Now you should start out with the position that you are wrong and need to come to God to be instructed in the truth.
For all have sinned and come short of the glory of God. The wages of sin is death but the gift of God is eternal life in Jesus Christ.
For the cause of Christ
Roger