Checked out schools camera. Dust issues should I say anything to the teacher or no?

So I checked out the schools Nikon D90 this weekend for a steelers game however I noticed when you look through the eye port I was having some dust showing up but it wouldn't show up in the pictures and in my stressed out state I used a Q tip on the censor to see if I could clear any dust which worked but there's still dust coming and going. So my question is when I turn in the camera on Monday should I say something to the teacher or just be quiet about it. I don't want to be held liable for "damages" i was going to because if your being open about it your not hiding anything but my friend said that they will say they checked it over before I got it and will try putting it on me.

The dust that you saw when looking through the viewfinder was not on the sensor. You will never see anything that's on the sensor when looking through the viewfinder. You could paint it black and still see through the viewfinder. What you saw was dust on the mirror and/or focusing screen. This is very common and just means that the school isn't maintaining their equipment very well. The dust can be easily and quickly removed with an air blower.
In the future, NEVER TOUCH THE SENSOR WITH A Q-TIP! Take a look at the pictures after you wiped the sensor with the Q-Tip and if they're fine or just have dust spots (small fuzzy spots) then go ahead and not only inform the school but downright complain about the poor condition of the camera and how it ruined your work and how much time you know have to spend cleaning up your shots. They'll probably apologize to you instead of accusing you of any damage.
Let this be a lesson to you - When ever you check gear out or rent it from a retail shop ALWAYS check the gear out before you leave. That way no one can wrongfully accuse you of damaging the camera.

It is just some dust on either the cameras mirror or focusing screen.

Do NOT attempt to clean the camera yourself.

Tell the instructor about it and they will either have it professionally cleaned or tell you not to worry about it.

Using a Q-tip on the sensor was the worst possible thing to do, especially since it is clear that the dust was not on the sensor (if it were, you would have seen it on the image files.

And YES, if you damaged the sensor using a Q-tip on the sensor, you will be liable.

There's NOTHING you can do to remove any dust on the cameras mirror or focusing screen. And the only thing you can do to remove dust on a sensor is to use a blower like the Rocket type blower to gently send puffs of air into the area of the sensor.

NOTE: If you keep the chamber behind the lens free of dust, then dust will not eventually migrate to the sensor itself.

Yes.

The problem with cleaning the sensor yourself is that by taking the lens off and raising the reflex mirror, you yourself introduced more dust to it. It would be best to have the camera cleaned at the service center where the technician can work in a "clean environment".

Tell the teacher that the camera is dirty and stop there.

When you see dust throught the viewfinder, you are NOT looking at the sensor. The dust you see is either on the mirror on one of the lens elements of the detachable lens.

Use a microfiber cloth or a bulb-style blower and your dust should disappear.

You should have not touched the camera sensor and just left it alone.
When you hand it back, just mention that it seems a bit dusty inside and let the authorities take it from there.

What you see through your view finder has nothing to do with the picture you take through your sensor. Little dust on view finder won't affect anything. Here, you could clean the surface with a soft cloth or a q-tip. If it doesn't remove it, leave it alone.

DO NOT touch the sensor with Q-tip! If you already did, you have likely scratched the very delicate surface of a special filter that is in place. Don't touch it anymore. Since your knowledge of this type of camera is very limited, I won't go into how to clean the sensor. This is not something you should be guessing and trying.

So only thing you can do now is to return the camera with a comment on dust on the view finder, and explain what you did to clean the sensor. Hopefully you did not cause any permanent damage.