Actually, a "key" refers to the tonal center of a piece of music, DO (as in DO-RE-ME). If you are singing or playing in the key of C, for example, C is your tonal center, or the 1st note and 8th note of the C scale. A C- major chord would then be C-E-G. It doesn't really sound like you have a problem singing "off key". You may need to explore and find out what keys are best for your voice. If your're singing in a group, it's perfectly all right to drop an octave if you need to. Are you an alto like me? I solved my range problem by learning to sing harmony.But you know, it's not as much about hitting the notes as it is singing for making a joyful noise and singing for the pure love of it.