Huh? Are you soprano or alto or do you have both ranges? What part you sing isn't necessarily how high or low you can go, but where your voice resonates the most. This changes the more you work with your instrument. Even though I can hit a high C (think Christine in Phantom of the Opera) I still tend towards alto. Test your range on a piano. To get a better idea of what sounds best, open your throat. To do this you raise your soft palate. Imagine a yawn. That part at the back of your throat (top) raises. Or imagine that you swallowed a golf ball an open up. Instead of scooping up to a pitch, imagine landing on it gently. This will help with flatness. At some pt it will be hard to keep your palate up. Sometimes it helps to change the vowel you are singing. Often times an Ah (open vowel) is easier to sing out of your comfortable range than an Ee (nasal vowel) is.