1393 Holy Communion separates us from sin. The body of Christ we receive in Holy Communion is “given up for us,” and the blood we drink “shed for the many for the forgiveness of sins.” For this reason the Eucharist cannot unite us to Christ without at the same time cleansing us from past sins and preserving us from future sins:
For as often as we eat this bread and drink the cup, we proclaim the death of the Lord. If we proclaim the Lord’s death, we proclaim the forgiveness of sins. If, as often as his blood is poured out, it is poured for the forgiveness of sins, I should always receive it, so that it may always forgive my sins. Because I always sin, I should always have a remedy.227
1394 As bodily nourishment restores lost strength, so the Eucharist strengthens our charity, which tends to be weakened in daily life; and this living charity wipes away venial sins.228 By giving himself to us Christ revives our love and enables us to break our disordered attachments to creatures and root ourselves in him:
Since Christ died for us out of love, when we celebrate the memorial of his death at the moment of sacrifice we ask that love may be granted to us by the coming of the Holy Spirit. We humbly pray that in the strength of this love by which Christ willed to die for us, we, by receiving the gift of the Holy Spirit, may be able to consider the world as crucified for us, and to be ourselves as crucified to the world. . . . Having received the gift of love, let us die to sin and live for God.229
You venial sins are cleansed at Mass when you receive the Eucharist. It is your mortal sins that must be confessed in the Sacrament of Reconciliation.1395 By the same charity that it enkindles in us, the Eucharist preserves us from future mortal sins. The more we share the life of Christ and progress in his friendship, the more difficult it is to break away from him by mortal sin. The Eucharist is not ordered to the forgiveness of mortal sins - that is proper to the sacrament of Reconciliation. The Eucharist is properly the sacrament of those who are in full communion with the Church.
possibly that is up to God, but you have assurance of not only forgiveness but absolution and reconciliation in the sacrament of penance.As a Catholic I put great store in the Sacrament of Reconciliation, or as we used to know it, Confession.
Can I be forgiven for my sins without attending Confession?