Don't let people complaining about the voice get to you, man. Nasty comments about mine got to me when I was a kid - singing for a performance when your voice is going through puberty is a bad idea - and it's been something I've been fighting ever since. Be proud of the fact you're willing to sing and put yourself out there. Besides, I love Bob Dylan, but if he could get where he is with how he sounds, you have nothing to worry about.