Good job overall, though there are a couple of things I saw that I think you could improve on. At the beginning of the demo you used at least three different lines that seemed to have the same voice, and something to keep in mind is that in a VA demo you need to try to show your range and the other voices that you have as much as possible, because it gets redundant after you use the same voice. But, you did start doing different voices near the middle which was good.
Also, you could add more emotion to some of your lines, because in some of them your voice was a bit monotone and it made it unconvincing at times, like when you went "I can't go on anymore, not after letting everyone down." you could add a little bit more emotion, just remember as a voice actor you want to make the character your voicing as convincing as possible.
Another thing to keep in mind, always do voices your comfortable with and that come naturally. Like the voice you did with "Ya'll laughed at me!" it sounded like you were struggling to do it and the laugh sounded like it was difficult to get out. If you really feel like doing a voice your not comfortable with, just practice with it until its gotten to a point where it becomes comfortable ( or if it never happens, you've just got to realize that you probably just can't do that voice :\)
Some good points are that you seem like you have a great range to start with in voice acting, you just need to practice voices and voice acting techniques as much as possible, because any practicing with voice acting helps to strengthen your voice and help you make the existing voices you have better. So I wish you the best of luck and I hope this critique helped :)