Simscape Multibody is a separate product from Simscape. You will need to install both if you want to use Simscape Multibody.
If your campus license has Simscape and Simscape Multibody on it (it should, that is fairly standard) then you should be permitted to install both. Perhaps try uninstalling and re-installing. If that does not work, contact technical support with your license number and they should be able to point you to the right resources.