The easiest way to fix a problem like this is to Recover an earlier save from the Load Game screen on the Main Menu. Hopefully you still have at least one backup save that was made before the problem occured.
If you can't do that, you could look for mods if you don't mind using them. I don't use them myself, so I don't know which ones to recommend.
Otherwise, you'll just have to try to pass the course without a presentation. I think that's fairly easy to do if you have joined an organization that provides extra credit for your major, reached the Seasoned Member level (level 2), and spend as much time as you can at the organization's events. Some of the events overlap with class times (especially the Brainiac's study sessions at the library) and I would recommend going to class over attending the event when that happens. You could also Study for the class using your phone, a computer, or a textbook. (You'll have to buy the textbook.)
Be sure to Email your professors on the phone or computer so you can track how well you're doing. I usually do that once per day, as soon as I can after the last class of the day. That way, you'll know how well your efforts at gaining extra credit or studying are paying off.
