Finding a perceived weakness in yourself is not objectively grave matter.
Furthermore, I don’t think this situation is a clear cut as you are making it out. Yes, a person might not be comfortable kneeling in front of a priest because they are utterly filled with the vice of pride. But in these circumstances, I think the majority of folks might simply be innocently shy, or maybe not want to make the priest feel uncomfortable, or feel as if they are drawing too much attention to themselves as being pretentiously pious, or any number of other, perfectly good reasons.
We don’t need to assume that our actions are, by default, mortally sinful unless we can prove that they’re not
We also shouldn’t treat our spiritual lives as if, unless we are utterly perfect, then we are almost always sinning gravely.
Our actions and choices are far more nuanced than that, and we should trust in God’s mercy and not feel as if He’s just sitting there waiting to damn us for every slight misstep.
Now, I’m not accusing you of having any of those attitudes; and, with regard to certain sins, I have often been guilty of them myself.
But if they resonate with you, and if you do find yourself thinking in those terms, I think it’s best to pray to God, to meditate on His love for us by contemplating the Passion of Jesus, and to leave things in His holy hands.
I’d also recommend you read this: mission.liguori.org/newsletters/pdf_archive/november2005sa_web.pdf