There is nothing wrong with getting assistance from the state if the conditions set out for that are applicable to you.
If the shortfall in your stipend will not affect your entitlement to assistance or its amount, then there is nothing wrong with that.
But if it will affect the amount, then you should look at what you are entitled to and take that only, and return the rest.
If you cannot return it, then you should donate it to the university where you are studying, or to some other public body.
And Allah knows best.