If you commit mortal sin do you have to go to confession the same moment you commit it? Or the same day? If you are really sorry but you plan to go on Sunday because pastor normally hears confessions on that day are you going to hell if you die before you go to the confession?
Ordinarily the Church would encourage you to go to Confession as soon as possible. If this means Sunday, then make a sincere act of Contrition, hopefully more because you are sorry for having offended God because of you love for Him, rather than simply because of the fear of going to hell. Personally, I would make an appointment to go to Confession sooner.
Fr. Vincent Serpa, O.P.