The vocal chords are a very delicate part of the voice and by not resting your voice you have damaged it and it will affect your range. When you sing higher notes the vocal chords vibrate faster whilst singing lower notes causes your vocal chords to vibrate slower, you can usualy feel this by putting your hand on your larynx and singing scales. i wouldnt recomend trying to hard to reach notes that you cant reach perfectly because it will cause your voice to strain, this will cause your voice to lose its frequency and power. when you sing the notes that your not able to reach just yet they sound very breathy to begin with but they can be strengthened with practice, if you find that you are overdoing it then rest. Singing loudly comes with practice most beginner singers start out with a quiet voice some louder than others, but placing the power over the range or tone of your voice is very foolish, if you find that singing loudly is hurting or straining your voice then its best if you sing at a lower volume untill your capable of singing louder, it basicaly takes years of practice to get your voice to sound better and to be able to sing with more power but that is minimized by protecting your voice.