Dear s,
You understand correctly. It is an additional mortal sin to receive the Eucharist in the state of mortal son. If you are in the state of mortal sin, go to the priest and ask him to hear your Confession. Don’t wait the whole week. You don’t have to wait until the time for Confessions.
You do need to make use of the sacrament. Confessing on you own requires that one make a perfect act of contrition. Contrition that is not based on one’s fear of punishment and only on one’s love for God is what we call perfect contrition. This is allowed when one is in danger of death and a priest is not available. But it is impossible for us to know how perfect our contrition is.
Fr. Vincent Serpa, O.P.