The Perkins loan is only for undergraduate students with extreme need. However what is extreme need? That is up to the school itself. Often it means that your parents have a low income and more than one student in school. If you are eligible for a pell grant you are more likely to be eligible for a Perkins loan. The Perkins loan is however, the best kind of loan to get for now, it has an interest rate of 5% fixed and lower fees than the stafford loan. However as time passes the interest of the stafford loan will decrease until it is only 3.4% and combined with the pell grant, that may be the better choice. It all depends on how much money you need for your expenses that year and what year it is.
If however you get a pell grant and do not receive the perkins loan and need more aid, go talk to your financial aid office. This is the one loan they have control and flexibility over. Do not, however, talk to the front desk person, make an appointment with someone behind the front desk, who has decision making abilities and you may get more help than you expect.