Whatsoever is not of faith, is sin. [Romans 14:23 KJV.]
All that believe are justified from all things [Acts 13:39 KJV.]
The question about purgatory can be answered by concentrating on justification by faith. If justification by faith be true, there is no need for a state (called 'purgatory') which is not mentioned in the bible.)
The question posits that what it terms 'repentance' and 'confession' is necessary to apply to each single sin, in order for each single sin to be 'forgiven'.
This is a legal concept and relies on legal works of self-justification.
It is not of faith.
(Therefore it is sin.)
To think that one can exonerate oneself of each single sin by applying the correct amount of remorse, or penitence, at the correct time (desperately, before one dies)
and the proper mode of confession in order to justify oneself . . . . is nothing to do with the gospel of Jesus Christ, wherein, Romans 1:17, is revealed (not the rightness of men but) the righteousness of God.
And that righteousness - of God - is revealed out of faith (it is ek) and unto faith (it is eis). Out of the faith of Jesus Christ ; and unto the faith of the believer.
God's righteousness (not man's superstition) is satisfied because it was demonstrated (see the special word for righteousness used in Romans 5:18 dikaioma, a demonstrated righteousness) upon his own Son.
By one (demonstrated) righteousness unto all humanity (under His headship) unto justification of life. [Literal Translation, see EGNT, with my brackets.]
The result of that demonstration of Divine righteousness was sufferings (he bore our sins in his own body on the tree, 1 Peter 2:24) and death (Christ died for our sins according to the scriptures, 1 Corinthians 15:3) and bloodshed (my blood ... which is shed for many for the remission of sins, Matthew 26:28).
That is how sins are remitted.
Not by the penitent's remorse, or fear, or terror as he feels his heart miss a beat and hurriedly tries to think whether or not he has confessed to every covetous thought, every lustful look, every envious sensation.
He that is entered into the rest (by faith) of God - has ceased from his own works, Hebrews 4:10.
Justification is by faith, not legal works.
And the gospel preaches that men are to give up all self-righteousness, of every kind (most of all the religious kind) and to depend utterly on God himself, through Jesus Christ.
With the heart man believeth . . . unto righteousness, Romans 10:10.
Righteousness, is of God alone. Humanity believeth.
And when that redemption (wrought out between the Father and the Son, through the eternal Spirit, Hebrews 9:14) is preached (by those sent of God to do so, who have experienced, themselves, the power of the gospel unto salvation, Romans 1:16) then the soul who believes, is advertised of the fact that all his sins have already been borne by Jesus Christ, the Son of God, 1 Thessalonians 1:10.
He is already delivered from wrath.
This, indeed, is a joyous sound. This, indeed, releases from legal terror and abject bondage. This is the silver sound of jubilee.
And, therefore, in believing that gospel, he is justified from all things whatsoever he hath done, Acts 13:39.
Thereafter he walks not by legal works, not by sight - but by faith, 2 Corinthians 5:7.
And there is no condemnation, Romans 8:1, to them which are in Christ Jesus who walk not after the flesh (in either worldliness or legal religion) but after the Spirit.
As to the steps of a son walking through this world, who is conscious of the eye of a father, 'My son, give me thine heart, and let thine eyes observe my ways (not legal ways),' Proverbs 23:26.
A father may chasten, a father may scourge, Hebrews 12:6, but it is not to condemnation, for the wrath is already past.
Be ye therefore perfect, even as your Father in heaven is perfect, Matthew 5:48. But no legal effort will achieve this. For whatsoever is not of faith - is sin. And the law is not of faith, Galatians 3:12.
This is the gospel.
What the question postulates, is something other than the gospel I find in my bible.
(Which is, I suppose, the reason that not one, single text of scripture is referred to by the question.)
I have answered this question as a lifelong Protestant, born into a household of four generations of Church of Scotland Ministers ; baptised, cognisantly and voluntarily, at the age of five, into that Protestant denomination ; then baptised as an adult at sixteen into the Baptist Assembly, another Protestant denomination ; then resident within Independent Protestant congregations for twenty five years ; and am now Director of Belmont Publications which publishes Protestant literature.