How can I show them what I got?

So, on Wednesday I auditioned for Fame the Musical (school play). Today were the call backs, and I got called back for Serena, Iris, and Carmen...I really want one of the lead parts! But, today I didn't feel like I did my best. Tomorrow are dance callbacks, so, what can I do to show the director that I am capable of pulling of a lead role. Please help..oh help I really want to be in it.