What is the ruling regarding my receiving two university scholarships at the same time, one of them by mistake, and what should I do about that?

If the scholarship system prevents obtaining two scholarships simultaneously, then you are not entitled to do so, based on the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions." If you have obtained two scholarships without knowing about this prohibition, there is no sin upon you. However, it is not permissible for you to continue receiving the funds, and you must inform the concerned party about it.