Financial aid is a combination of loans, grants and work-study programs that provide for your education and living expenses. The amount of financial aid you are eligible for is determined by your prior year's tax statements (in other words your income). From there the government decides how much they will aid you with and how much you need to pay out of your own pocket. Student loans that are received through your FAFSA application are backed by the government. That basically means that regardless of your credit worthiness you will receive the money necessary to attend school so long as that is your need.

It seems to me that due to your income you are not eligible for enough financial aid to cover all of your costs. The school has no idea what will come back from your FAFSA until they get those numbers... then, and only then can they tell you whether all your expenses will be covered for sure. They have ways of figuring it out before hand but I've been told that my financial aid will cover it and then have received a bill (at a different school, not UoP)... it happens sometimes. And it sucks. Boy do I know it sucks but you move forward. You pay the remainder of the bill and get it done with. It really is a small amount when you consider UoP is around $14,000 for a 4 year degree. BTW, I WISH my tuition was that low...

Good luck with your education.