I’m from a liberal wing of the Reformed tradition, so I’m not sure whether this answer will be the same as for traditionalists, but maybe.
Jesus uses the term “repent” to refer to changing the direction of your life.
The Reformed tradition cares more about sin than sins. Sin being our orientation, our inability or even lack of desire, to do the right thing. Individual sins are a result of this. There, too, what matters is the change in direction, accepting responsibility for sins and changing motivation away from self to others and God.
Repentance, then, is more that change in direction than being sorry for individual sins. Obviously someone who is repentant in this broad sense will also accept responsibility for specific sins and thus be repentant there. But if you focus primarily on having to repent from every sin, it becomes legalistic, a "work" as you say. God is not sitting there with a list of sins, ready to punish us if we miss one. The worry that he might be (as well as a concern that repentance doesn’t count unless it’s perfect) was one of the primary concerns Luther had before his enlightenment.
It’s interesting to note that Jesus doesn’t refer to sins, except their forgiveness. He speaks of judgement a number of times, and that can be based on mistreating people or not showing fruit, He talks about various things we aren’t supposed to do — though he tends to focus on intent. But he doesn’t actually talk about sins as a category, except their forgiveness. He certainly does talk about repentance, as changing from someone who is opposed to God’s way of life to one who is follows it.
Paul is more focused on individual sins. I conjecture that this is at least in part because he was dealing with converts from a pagan background with appallingly different standards for behavior. Still, while he expects his converts to follow Christians standards of behavior, he doesn't set up this expectation that you have to be sorry for every sin you have committed or you're in trouble. He also uses the term repent primarily for a change in direction.