I have a student loan

The regulations at 34 CFR 682.207(b)(1)(v)(A) require lenders to disburse federal education loans directly to the school. Per 34 CFR 668.164(d), the school may use the proceeds to credit the student's account at the college to pay for current year charges for tuition and fees, room and board, and up to $200 in prior award year charges. If there is a credit balance the school must disburse the excess funds to the student within 14 days.

School-certified private student loans are treated in a similar fashion, with the lender sending a check to the school.

Direct-to-consumer private student loans, on the other hand, send the check to the student.

Books and supplies are included within the definition of cost of attendance, so one can obtain student loans to cover the cost. If the credit balance that was refunded to you is insufficient to cover these costs, you may need to obtain a larger loan. Or if you are referring to a private student loan, it is possible that the lender restricted the loan to just the college's charges (a common anti-fraud measure).

I recommend that you talk to the financial aid office at the college if it involves federal loans or school-certified private student loans, and the lender if it involves a direct-to-consumer student loan.