Being nervous about driving is very common. Its one of those things that gets less scary the more you do it. Get as much time in the drivers seat under supervision as you can. Can you work up to it each day? Day one sit in the car somewhere, day 2 sit in the drivers seat, day 3 adjust mirrors to your requirements, day 4 keys in the ignition etc etc
Sometimes having smaller goals makes it easier to achieve.

Goodluck