How can I check my own understanding in comparison to the Bible, if I misunderstand the Bible itself.
"Therefore do not be unwise, but understand what the will of the Lord is" (Ephesians 5:17).
The first point to realize is that the Bible is understandable. Yes, people do twist the teachings of God, but the fault lies with the ones doing the twisting and not with what is actually said.
"as also in all his epistles, speaking in them of these things, in which are some things hard to understand, which untaught and unstable people twist to their own destruction, as they do also the rest of the Scriptures" (II Peter 3:16).
Here then is the reason the Scriptures are misunderstood: either the person is untaught or the person's thinking is unstable. An untaught person makes assumptions about what God has said without ever verifying his facts. He tries to operate without all the information, and unsurprisingly, he makes mistakes. The unstable isn't interested in the truth. He has his mind already made up and it doesn't matter whether his ideas are logical or fits what the Bible says, he'll find some twisted way to make it fit. Both have a common flaw: the person is using what he wants to be the standard for deciding what the Scriptures say.
"And so we have the prophetic word confirmed, which you do well to heed as a light that shines in a dark place, until the day dawns and the morning star rises in your hearts; knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit" (II Peter 1:19-21).
Rather than approaching the Bible as proving what I already believe, God says it does its own interpretation. That means I have to approach it as learning what it teaches and then molding my thoughts to Gods. It is when we go the other way around that we get into trouble.
So when you find an idea, you check to see that it is consistent with the context in which it is presented and that it is consistent with the other teachings in the Bible. If you find a conflict, it means you misunderstood something somewhere. Sometimes figuring out what is sometimes hard. That is where other Christians help. It is one reason why going to a sound church is important.
"And He Himself gave some to be apostles, some prophets, some evangelists, and some pastors and teachers, for the equipping of the saints for the work of ministry, for the edifying of the body of Christ, till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ; that we should no longer be children, tossed to and fro and carried about with every wind of doctrine, by the trickery of men, in the cunning craftiness of deceitful plotting, but, speaking the truth in love, may grow up in all things into Him who is the head -- Christ -- from whom the whole body, joined and knit together by what every joint supplies, according to the effective working by which every part does its share, causes growth of the body for the edifying of itself in love" (Ephesians 4:11-16).