and that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus
The sacred writings known to Timothy at the time Paul wrote to him. No writings beyond that are needed to give the wisdom that leads to salvation through faith. And as verses 16 and 17 say, these same sacred writings that existed and were known to Timothy are also complete to provide guidance of Christian actions (correction) and to teach and evangelize. That is EXACTLY what it says.
Thus - in the words of Paul, in his 2nd letter to Timothy, the Scriptures are all that are needed for salvation; however, having additional reflections, concordances, expositions on the Scripture can help. But fundamentally, they are NOT needed.
Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and [of] the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again. The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit. - John 3:5-8
But as many as received him, to them gave he power to become the sons of God, [even] to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. John 1:12-13
But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know [them], because they are spiritually discerned. - I Corinthians 2:14
Why do ye not understand my speech? [even] because ye cannot hear my word. John 8:43
Actually, Paul is referring to the sacred writings that existed from the time of Timothy's childhood:
...from childhood you have known the sacred writings which are able to give you the wisdom...Using your interpretation excludes a lot--or all--of Paul's writings. And how old was Timothy? If he's older than the Gospels, your interpretation might well exclude them too.
Thus your interpretation must be rejected.
And still no sola Scriptura.