I could be wrong but you can’t serve with mortal sin secondly not to ask you put your sin on display but you’d be real hard pressed to commit a mortal sin.
No really, it’s really hard to commit a mortal sin. The evil intent alone is hard enough to muster but the sin itself has also to be very grave.
The easiest mortal sins I’m aware of are breaking laws that would invoke jail time, missing mass or already having a mortal sin and having a sacrament and most sins regarding sex.
That’s surprisingly a very narrow list.
Remember the requirements
It’s gravely wrong, you know it’s wrong but you are going to do it anyway.
If there is any doubt or uncertainty or outside compullustion it muddies up the water quite a bit and it becomes hard to tell. If you are not sure or you don’t know what else you could have done or did something on impulse or snap call its prolly not mortal.
Not to downplay sin but let’s be realistic here.