Salvation is either 100% of God or there is some amount of cooperation on the part of the sinner. Jesus either paid the price in full, or there is still some work to be done.
The Catholic model of salvation is one of cooperation between God and the sinner. Jesus’s perfect righteousness and death on the cross merited the grace for the sinner to justify (make righteous) himself.
This grace merited by Jesus (sanctifying grace) is given in increments starting with Baptism and is continued to be merited by the sinner through good works (sacraments, acts of charity, etc.). But sanctifying grace can also be lost through sin, and if you die without sanctifying grace in your soul, you will not make it to heaven.
"Once you have supernatural life, once sanctifying grace is in your soul, you can increase it by every supernaturally good action you do: receiving Communion, saying prayers, performing the corporal works of mercy. Is it worth increasing sanctifying grace once you have it; isn’t the minimum enough? Yes and no. It’s enough to get you into heaven, but it may not be enough to sustain itself. It’s easy to fall from grace, as you know. The more solidly you’re wed to sanctifying grace, the more likely you can withstand temptations.
And if you do that, you maintain sanctifying grace. In other words, once you achieve the supernatural life, you don’t want to take it easy. The minimum isn’t good enough because it’s easy to lose the minimum. We must continually seek God’s grace, continually respond to the actual graces God is working within us, inclining us to turn to him and do good.” Catholic.com
"Grace is the help God gives us to respond to our vocation of becoming his adopted sons. It introduces us into the intimacy of the Trinitarian life." CCC 2021
"We can have merit in God's sight only because of God's free plan to associate man with the work of his grace. Merit is to be ascribed in the first place to the grace of God, and secondly to man's collaboration. Man's merit is due to God." CCC 2025
"No one can merit the initial grace which is at the origin of conversion. Moved by the Holy Spirit, we can merit for ourselves and for others all the graces needed to attain eternal life, as well as necessary temporal goods." CCC 2027
"We can therefore hope in the glory of heaven promised by God to those who love him and do his will. In every circumstance, each one of us should hope, with the grace of God, to persevere "to the end" and to obtain the joy of heaven, as God's eternal reward for the good works accomplished with the grace of Christ..." CCC 1821
Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion. Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life. Even temporal goods like health and friendship can be merited in accordance with God's wisdom. These graces and goods are the object of Christian prayer. Prayer attends to the grace we need for meritorious actions. CCC 2010
"The preparation of man for the reception of grace is already a work of grace. This latter is needed to arouse and sustain our collaboration in justification through faith, and in sanctification through charity. God brings to completion in us what he has begun, since he who completes his work by cooperating with our will began by working so that we might will it: Indeed we also work, but we are only collaborating with God who works, for his mercy has gone before us." CCC 2001
"The merit of man before God in the Christian life arises from the fact that God has freely chosen to associate man with the work of his grace. The fatherly action of God is first on his own initiative, and then follows man's free acting through his collaboration, so that the merit of good works is to be attributed in the first place to the grace of God, then to the faithful. Man's merit, moreover, itself is due to God, for his good actions proceed in Christ, from the predispositions and assistance given by the Holy Spirit." CCC 2008
This cooperation with God by the sinner to ensure salvation is quite different than the Protestant understanding of justification which relies on the completed work of Christ on the cross to reconcile the sinner to God (which is obtained by faith alone).