It sounds like you may be the representative payee for your brother. If you are the representative payee you must be able to show how the money was spent and to show a reason why you spent the money that way. In this case your actions seem reasonable but SS can still review bank statements to verify the expenditures. I would also try to obtain a statement from the doctor's office that says that you initially thought that it would only be a short stay. The more independent corroboratoin from third parties, the better.
This information is provided as a public service to provide a general answer and should not be relied upon as legal advice.