Oh god, I do feel your pain. I learned to drive 12 years ago and I've driven almost every day since then, including into central London every day for work, but I still panic at the thought of driving for 30 mins on the local A road, to go and see my sister.
I do the Google maps thing too, I even write down instructions for myself in case I get lost!
It's silly really, I'm an experienced and (mostly) safe driver, so I don't know why I panic about going on an unfamiliar journey, it's not like I'm going on a bloody safari, it's the wilds of Kent, it's actually quite hard to get lost, even on the confusing roundabouts and slip roads.
I think that sometimes, you just have to push yourself to go out and do it. You've been driving for almost half of your life. Statistics show that women are better drivers, we don't take silly risks and we don't tend to show off, especially with our kids in the car. You're going to plan your route carefully, but even if you take the wrong turn-off, it's not a big deal, you can always go another way. It's not likely that you'll cut someone up, but if you do, so what? You'll get a beep, and possibly a rude gesture/swear word or two...welcome to my world (everyone drives like a dick in London...including me!)
You can do this, you know that you can. It's a confidence thing, you just need to give yourself a kick up the backside!