I was recently in a collision and not sure what to do?

If you only had liability, no matter what happened, insurance is not going to cover it. Liability coverage only covers people. Full coverage is when you include Collision and Comprehensive. In your case you would have needed comprehensive. The excuse the guy gave you is complete BS. It doesn't matter if it was locked or not or kept closed by a twist tie. You're pretty much screwed and have to pay for it yourself. If you want, you can sue the school for neglect but its a long shot.