I'm having the same problem. I passed a month ago after a year (long story, I'm bad but I'm not that bad) of learning and my dad, despite knowing that I planned never to drive again, bought me a car. I have absolutely no interest in it whatsoever and make near-fatal (I'm not joking) mistakes every time I drive the damn thing, but he won't let me use public transport any more if I want to leave the house. Don't get me wrong, I tried my hardest at first to remain at the standard at which I passed but in my case, practise definitely does not make perfect. Long story short, without my instructor next to me I don't know **** and to be honest, won't ever know ****. The astonishing quality of my driving even after a year is starting to bore even me. Take today, for example - I counted my exit on a roundabout as the fourth, for some reason it turned out to be the third, my dad alerted me at the very last minute but as there was a temporary red light and vehicles were flowing from the exit back out onto the roundabout, I panicked and instead of waiting tried to cram myself next to a van. Yeah. Not only that, but I cut in front of an ambulance that I wasn't aware of and cut in front of it again very dangerously reversing of the exit to continue 'round and take another one. Not only that, but the purpose of the trip was for some discounted petrol, only I saved about 4p and faced my car the wrong way so put petrol everywhere but inside. I have had a year's worth of training for this, and for what? Money down the drain, mate. I drove better as a learner. No fear - I've now resorted to leaving my car unlocked in the hope that somebody snatches it. I'm not joking. So know that firstly, it's not just you and secondly, no matter how bad you are, you can't be as bad as me. I mean, don't even get me started on my parking -
As for what I'd recommend, definitely drive with a (sensible) friend with some driving experience. You'll feel much more relaxed, particularly if you turn on the radio (on a low volume), chat a bit when you can, etc. Driving with a parent to me is like sitting my test all over again, but I drive much better with a friend or sibling acting as a second pair of eyes, a GPS and a non-judgemental presence. Also, it sounds odd but I even prefer driving alone sometimes, it's a huge weight off my chest to do my own thing in my car and take it slow and steady by myself. Don't push yourself to journey too far too soon, stick to places you know well at first just in case - and most importantly, don't drive if you're not feeling up to it. Having a panic mid-journey is not fun, so if you're brain's like "nah, mate," then nah, mate. What's the rush?
(Also, sometimes your level of skill is your level of skill. Don't put too much pressure on yourself to be the next Lewis Hamilton. I'm for sure not getting any better than this, lol.)
Best of luck, I'm sure that you'll be absolutely fine! ♥