Q. What is the problem with "extra references"?
For work to be submitted to the IBO, your bibliography (or works cited or reference list) must only contain sources you have actually cited in your paper.
Any sources you have read, but have not mentioned in the paper should not be included.
In other situations, your teacher may ask you to include a "works consulted" list. That can include everything you have read that relates to the topic, whether you cite the material or not.