Why did my school reduce my salliemae loan?

Perhaps that is because they only covered the cost of tuition/expense from their end. Often times you need to contact your school's financial aid department and tell them to process the loan for the maximum amount/full cost of attendance or for $3,100 extra (whichever you prefer/approved). If they ask what you need the extra money for simply tell them what you have stated. Obviously attending school requires food expenses, books/supplies, computers/ink, transportation, etc. It shouldn't be an issue as you were approved for more. It just can't exceed the maximum amount of the school.

For example, if your school tuition/expense was $2,000 and your school has a maximum amount/cost of attendance of $4,000 you would only be able to get $2,000 more. Usually the amount is what you would be charged for dorms added to the tuition but as a commuter you can use that amount for other related expenses.