When you become a catholic you find lots of new ways of feeling guilty.
Here's the way that I look at it: if you are very new in a conversion, the broad strokes (adultery, fornication, atheism, murder, mayhem, theft, etc) are what you feel really guilty about and what you are worried about changing. As you mature, you start recognizing things within yourself that are not pleasing to God that you would have been utterly blinded about earlier.
Consider:
[Eph 4:22 KJV] That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; [Eph 4:23 KJV] And be renewed in the spirit of your mind; [Eph 4:24 KJV] And that ye put on the new man, which after God is created in righteousness and true holiness.
I think that if you'd ask most Catholics, they would say that this is a process, not a one time event. As you continue to put more of the "new man" on, you will need to shed more of the "old man."
That is why even the greatest saints through history made frequent use of the Sacrament of Penance. Not necessarily because of horrible sins that they keep doing, but because even more minor sins / vices become even more offensive as time goes on. And, yes, part of that process is, as you recognize more areas where you fall short, you feel guilt for that.
Christ died for ALL of our sins, not just the big ones.
Then there is no need for penance.