Missing Information In Thesis
If your thesis was accepted and you have your degree, there is no "action" that can be taken against you. You can, however, produce a new publication giving the "missing" background of your original study. 

Even better would be to extend your work, and maybe your model and explain in a new paper the new work, encompassing the old. 

Just be careful to cite the old work, especially since it has been "published" on the website. That will probably make it impossible to republish that, but makes it even more possible to derive new work from it. 

But any "blame" for missing parts is not yours alone, being shared with your advisor and any committee that accepted the work. But, in fact, I don't think there is really any blame to share. Move on. Do even better work.