my lowest note is C3 and im a 12 year old girl

That's great! C3 is a good starting point for a 12-year-old girl. As you continue to develop and practice, you may discover that your vocal range expands, allowing you to sing even lower notes or reach higher ones. With proper training and exercises, you can further develop your voice and expand your range as you grow older. Keep practicing and working with a vocal coach or teacher to get the most out of your voice.