Christ made our reconciliation on the Cross.
We are saved by Grace through Faith and not by works.
Ephesians 2:8 Catholic Edition 8 For by grace you have been saved through faith, and this is not your own doing; it is the gift of God—
We confess our sins to him but he has reconciled himself to us.
Romans 5:10
For if while we were enemies, we were reconciled to God through the death of his Son, much more surely, having been reconciled, will we be saved by his life.
2 Corinthians 5:20
So we are ambassadors for Christ, since God is making his appeal through us; we entreat you on behalf of Christ, be reconciled to God.
Colossians 1:21-23New Revised Standard Version Catholic Edition (NRSVCE)
21 And you who were once estranged and hostile in mind, doing evil deeds, 22 he has now reconciled[a] in his fleshly body** through death, so as to present you holy and blameless and irreproachable before him— 23 provided that you continue securely established and steadfast in the faith, without shifting from the hope promised by the gospel that you heard, which has been proclaimed to every creature under heaven. I, Paul, became a servant of this gospel.**
But according to the chatechism, one should make a perfect act of contrition in order to be able to recieve communion if they had commited a mortal sin and cannot make it to confession before they go to mass that week. What should someone do then?