Canon 841 merely says that the Muslims are "included" in "the plan of salvation". But not far from is, Canon 836 says that "All men are called to this catholic unity of the People of God. . . . And to it, in different ways, belong or are ordered: the Catholic faithful, others who believe in Christ, and finally all mankind, called by God's grace to salvation." Canon 841 also acknowledges that the Muslim, compared to the pagans or the Atheists, adore God the Father, so that is, relatively to the others, helpful to them. The thrust of the paragraph is that everyone is called to salvation, because the Church was told to "baptize all nations".
Canon 846 explains that whenever one is saved -- and we don't know who is and who isn't -- he is saved as a member of the Body of Christ which is the Catholic Church. If a Mulsim refuses to his last breath to enter it, he cannot be saved, and if a Protestant refuses to his last breath to enter it, he cannot be saved, and if a Catholic refuses to remain in it, he cannot be saved either.
This is the relevant chapter "I BELIEVE IN THE HOLY CATHOLIC CHURCH"
Your mistake is to read 841 as if the acknowledgement of the Creator is sufficient to enter Heaven. Canon 841 does not say that. The root of your mistake is probably the belief common to many Protestants, that a particular set of beliefs is both necessary and sufficient for salvation. The fact is, we are not saved by faith alone, -- faith of any kind.
841 in its entirety:
The Church's relationship with the Muslims. "The plan of salvation also includes those who acknowledge the Creator, in the first place amongst whom are the Muslims; these profess to hold the faith of Abraham, and together with us they adore the one, merciful God, mankind's judge on the last day."
Salvation, according to the Catechism, includes those who acknowledge God, and that is all that is needed to reach Heaven. It does not say that they must accept Jesus or the Church.
Canon 846 explains that whenever one is saved -- and we don't know who is and who isn't -- he is saved as a member of the Body of Christ which is the Catholic Church.
Assuming this is correct, then all Protestants who have given their lives to Jesus are part of the Catholic Church, correct?
if a Protestant refuses to his last breath to enter it, he cannot be saved,
Oops. Only if the Protestant becomes Catholic apparently. Which contradicts the statement you just made:
Canon 846 explains that whenever one is saved -- and we don't know who is and who isn't
Apparently, if you die a Protestant the Catechism states you are not saved. According to your own words. You must accept the Catholic Church as supreme or you will not be saved.
Again, this is the biggest issue I believe most Protestants have with the Catholic Church: it is now the sole arbiter of who shall be saved and who is condemned, by virtue of controlling who is a Catholic. And most Catholics refuse to honestly admit this position, trying to shade it in ecumenical terms.
Fundamentally, non-Catholic believers in Jesus are not saved; believers in God but not Jesus (even if taught and aware of Jesus and the Bible) are saved. And the Pope and Church Heirarchy have become the gatekeepers to salvation and Heaven.