Is everything in the Bible true?
Everything that the human authors of Scripture affirm to be true is true, in the sense in which the human author meant it.
This is not the same thing as saying that everything in the Bible can be taken literally. If the inspired Biblical author uses a figure of speech, or states an approximation, or writes in a non-historical literary genre — to name a few examples — then these factors must be taken into account in order to ascertain what the author is, and is not, affirming as true, and in what sense the author means what he says.
This is easier said than done, which is why we need to read Scripture in light of how the Catholic Church has understood it down through the centuries.