I think all that really matters here is that God is both perfectly just and perfectly merciful. As I’ve grown in my faith over the years, I’ve come to realize that letting go of sin is about freeing your heart a bit more inch by inch to give more and more of your heart to God. Its a lifelong process. Repentence is letting go and handing yourself over to God’s mercy and thus fully accepting it. A lack of repentence is clinging to the sin.
As such, I just look at the qualifiers for a mortal and venial sin for trying merely to figure out if I should not go up to communion before I go to confession. I also look at it when prioritizing what sins to confess. When I’m in doubt, I don’t go to communion and even if I committed a grave sin but have reason to think I was lacking in total consent, I still feel the need to rush to confession ASAP not because I fear God’s wrath, but because I want the grace to avoid becoming attached to that sin. I look at it as a learning opportunity. I try not to worry myself about the technicalities. All I can do is educate my conscience, prayerfully examine it realize that when I go to confession I’m confessing it to the best of my knowledge. If I am to grow to examine my conscience any better than that, it is through the grace of God.