The Constructive stuff first. For a demo you want a scene not just a voice, also you need to space this out. it's very hard to tell where one voice started and another ended. in reality casting directors only listen to 30 seconds of a demo, also a bit of music will give some more personality to your voice, as well as the scene. most importantly do lose the thanks for listening to my voice demo part. you it to sound as professional as possible.
The Good stuff second: You have a great range, very close to Billy West, as well as Greg Ciphes. It's good that you smile when you record, which is super important for the comedic roles you said you wanted, your mic seems to be good quality as well.
Keep practicing, record every day, read books, take acting lessons, go to workshops, study theater, know who's in the business... finally dont get into voice acting for the money, get into it because you love doing it.