How to expand your range?

I am better at the loud, somewhat high parts. People find that hard, but I can barely sing anything else! I sing the Star Spangled Banner at every school function, but that is like the only song I can sing. I am loud, but I have a horrible range. My dad (a musician for his whole life) says I am singing in the wrong octave. I need help expanding my range and finding the right octave! I don't have the money for vocal lessons...