Communion is a faith increasing ordinance, not a doubt increasing one.
When we come to the Lord’s table, if we are thinking correctly, we remember our sin. But staring at our sin nourishes doubt. When we look at the bread, we are encouraged that the debt our sin incurred is no longer outstanding. There would be no bread unless another’s body had taken our judgment. We eat because Christ paid the penalty in full and we are forgiven. When we look at the cup, faith is strengthened as we remember that a sacrifice has already occurred. The cup means God is not waiting to satisfy righteousness with our blood. We drink because Christ freed us from guilt.
Do you have faith? If no, repent and believe. If you do have faith, even the size of a mustard seed, you are forgiven and free. Participation in this meal is a feast for faith, not a fast to prove we have it.