You only know your own conscience. If you are truly are in mortal sin, you ARE compltetly seperated from God…please call the rectory and go to confession on a lunchbreak.
However, if the sin was only questionably mortal, please don’t fear. Mortal sins are pretty hard to do (much harder than some on this board suggest). There are severe venial sins and those are EASY to commit. However, they do not cut you off competely from God. Mortal sins also almost always carry grave social ramifications. I actually cannot think of one mortal sin that can be fixed by simply repenting in your heart.
Again, I don’t know your sin or your consince. It’s up to you what you do. But if you are speaking the truth, see the sin as literally having you heart beating outside your body. Spiritually, you’re clinically dead. It’s serious stuff…if it’s a mortal sin.