What makes you think everything is in the Bible? The word “trinity” isn’t in the Bible. The Bible doesn’t say, “Believe the Bible.” Your argument doesn’t hold for basic reasons. The Bible, as a single volume, didn’t exist until over 400 years after the Resurrection. The books of Bible were assembled into the volume, thus impossible to reference themselves as a volume.
Should you choose, you can read any of the number of works, freely available on any number of Catholic websites (Vatican.va, EWTN.com, Catholic.com) that clearly demonstrate the Biblical references for every Catholic belief.
You are free to believe what you want, but that doesn’t mean you are free to tell the Catholic Church what it believes and teaches.
“The word “trinity” isn’t in the Bible.”
So what. However, it is clear from the Bible that God, Jesus, and the Holy Spirit are three in one.
There is so much error here, it is difficult to know where to start. But, I will try. First, the Scriptures do actually say to "Believe the Bible". II Tim 3:16ff, "All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness that the man of God may be adequate, equipped for every good work." Again, please read that Bible...the RCC does not teach what is in it.
And, again, you are incorrect about the Bible existing 400 years after the resurrection. The entire Hebrew text existed during Jesus' day. He referred to it multiple times. The balance of the texts were done no later than 92AD (likely I II III John). But, the descriptions of the "real Gospel" are clearly mapped out by Paul in Romans (circa 57AD). And, by this point we Gentiles are grafted in and the material is directly pointed at us (notice Eph. 2).
But, I still ask you which of the errant doctrines I mentioned as promulgated by the RCC is actually taught in the Scriptures?
Would you then show the scriptural reference for the apostles teaching the assumption of Mary?