I am not a lawyer, nor have I ever directly worked in professional video production.
In a typical situation where, say, a cameraman is working for a production company which is then in turn being contracted by some other entity, the cameraman would likely have no rights to the footage he shoots, but there would probably be a clause in his contract that grants him the right to use footage in a portfolio.
The production company then negotiates with their client to decide if the client will own all raw footage at the conclusion of the project, or just the finished product.
If your situation doesn't have any contract in place that mentions ownership, well, that's not a situation I'd want to be in. If you are single-handedly being contracted to shoot, produce, and deliver a finished video to the company, then you may have rights to the footage. However, if the company is producing the video in-house and you are simply there to shoot for them, you probably don't have rights to the raw footage. On the other hand, if this is a placement for a college course, then it may actually be YOUR SCHOOL that owns the rights to your raw footage. You'll have to find that out.
You should NOT watermark anything unless you have signed something that specifically allows you to do so. This will just make people angry, and that's not good for anyone unless you're prepared to enter a costly legal battle.
The fact that you are holding all of the raw footage right now does not necessarily mean you have the rights to it.
Frankly, the fact that this is an academic placement (and therefore unpaid, I imagine) makes me think the "generic contract" you signed essentially means YOU do whatever THEY want, and you get a grade for it. End of story--they own the footage. And besides, when have you EVER seen cameramen credited on the footage they shoot? Only at the ends of feature films, and in the cameraman's own portfolio; never on a promotional video.
Nonetheless, I do believe you are justified in wanting to retain the use of your footage for your professional portfolio. If they are going to begrudge you that, I think you have a fair case to make as a student, and your advising professor should be able to vouch for you and bargain on your behalf.