Voice Over Troubles

Today i also recorded my dad reading the voice over script that i am going to use at the begining of the film. I recorded him reading the script 21 times, yet his voice does not match the script and is not able to make the voice over sound as good as it could be. This is a problem, because i need someone that can do American accents. I have tried recording myself speak, but it does not sound like an adults voice and as a result ruins the feel of the film.