You can try to make an act of perfect contrition.
This means that in addition to ‘stopping’ whatever mortal sins you are committing, that you thoroughly repent them, NOT ‘just’ because you might go to hell (of which you’re worried) but totally, freely, and sincerely because these sins offend God. IOW, you take ‘you’ totally out of the equation and focus directly on God. Repent, not because of sin’s effect on YOU, but because of sin’s effect on God.
This is very difficult—to stop, and to focus on God and not self–but it is not impossible. You may have to work at this, and pray, over and over, for God’s grace. And you won’t ‘know’ you are free until you do have a sacramental confession. . .but you must still try to be perfectly contrite, even without that assurance. IOW, you must have faith, yet not presume.
I will pray for you. Listen to John Paul II (“Be not afraid”) and to St. Pio (“Work, pray, and don’t worry”) and above all to Jesus ("Come to me, all who labor and are heavy burdened, and I will give you rest), fix your mind and heart and soul on God and loving Him totally, and let Him take care of you.
God bless.