Actually, Catholics are are allowed a certain amount of freedom in the interpretation of scripture. The Church rightly sets the boundaries and guidelines for this interpretation. One cannot interpret scripture for themselves and go outside of the boundaries of Christian teaching. The Judaizers, the Gostics, the Donatists, the Nestorians, and others did this very thing. They were refuted and condemned for doing it.
Scripture even tells us that private interpretation in the fashion discouraged by the Church is wrong.
The apostle Peter says the following:
2 Peter 1:20-21
First of all you must understand this, that no prophecy of scripture is a matter of one’s own interpretation, because no prophecy ever came by the impulse of man, but men moved by the Holy Spirit spoke from God.
2 Peter 2:1-2
BUT FALSE prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Master who bought them, bringing upon themselves swift destruction. And many will follow their licentiousness, and because of them the way of truth will be reviled.
2 Peter 3:15-17
So also our beloved brother Paul wrote to you according to the wisdom given him, speaking of this as he does in all his letters. There are some things in them hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other scriptures. You therefore, beloved, knowing this beforehand, beware lest you be carried away with the error of lawless men and lose your own stability.
These are not the only verses of scripture that can be brought to bear on this topic, but they should be sufficient to give any person arguing “sola scriptura” food for thought and reflection.
Every non-Catholic Christian Church has traditions that guide them in their understandings of scripture even if they are not willing to admit it. Non-Catholic Christian fellowships did not get their understanding of the “Trinity” strictly from their personal reading of scripture. You need to choose your teachers carefully and you need an authentic teacher.
The apostle Paul has this to say about teachers:
2 Timothy 1:11
For this gospel I was appointed a preacher and apostle and teacher,
1 Timothy 3:1-2
THE SAYING is sure: If any one aspires to the office of bishop, he desires a noble task. Now a bishop must be above reproach, the husband of one wife, temperate, sensible, dignified, hospitable, an apt teacher,
Titus 1:7-9
For a bishop, as God’s steward, must be blameless; he must not be arrogant or quick-tempered or a drunkard or violent or greedy for gain, but hospitable, a lover of goodness, master of himself, upright, holy, and self-controlled; he must hold firm to the sure word as taught, so that he may be able to give instruction in sound doctrine and also to confute those who contradict it.
2 Timothy 3:14
But as for you, continue in what you have learned and have firmly believed, **knowing from whom you learned it **
These passages show who our teachers are in doctrine and in the word of God found in scripture. These teachers are the bishops who are the successors of the apostles. We are not self taught by simply reading scripture on our own. Likewise, “we are not to have **itching ears **and seek out teachers to our own liking.”[2 Timothy 4:3-4]
I hope this helps to answer a couple of your unanswered questions.