That's why you should pick ONE regular small simple journey and just practise, practise, practise it till you can almost do it without thinking. Go out v early in the morning or once the days get longer, go in the evening after rush hour. Then add another journey with maybe a more complicated junction or two and add that to your "repertoire". Then another. Just work your way up that way slowly doing longer journeys, building up to going at busier times.
A decent sat nav is a total game changer. My car has Apple Car Play and I just use Apple Maps. DH prefers Google Maps. I love seeing which turning you need on a roundabout for example. Just knowing that if you miss a turning it will re-route you ensures you don't panic. And if for some reason you lose your sat nav signal or phone dies and you don't know where you are, just pull over somewhere convenient so you can pull your thoughts together and make a plan. Ask a passerby if necessary. Maybe have a paper map in the car as a backup so if necessary you can figure out if you need the westbound or eastbound direction, for example, and if a city is mentioned you know where that is geographically so nknow you're heading in roughly the right direction.
Motorways are fine, honestly, you just need practice merging on and off. Some are quieter than others. And again, go at quieter times. And just practise going on and off junctions, navigating big roundabouts etc.
I was a VERY nervous driver learning to drive and even for a few years after passing my test. I don't particularly enjoy driving in busy city centres I'm not familiar with as everyone else seems to know where they're going and there are constant lane changes and bus lanes etc which you're unaware of till the last minute, but often people will let you move over to the right one if you indicate if you're in a queue for the wrong one.
Always have plenty of fuel in the car! Then you'll never be stressed that you've taken a wrong turn but are about to run out fuel. Even if you're heading miles the wrong way up a motorway you'll be just fine with plenty of fuel, as you'll be able to come off and get back on at some point.