First of all congratulations on your pass and your new job. My reply is also written assuming you are a woman and my take on it, based on recent experience, and being a woman, is this: You say you seem to do OK most of the time, so that’s actually quite positive, no? What you want is to do OK or more than OK all of the time, so you’ve not too far to go. You also say that you got really flustered when you blocked an entrance while manoeuvring I wonder if it is more about confidence and less about spatial awareness.
If I may be permitted to make a sweeping generalisation, women are brought up to take up as little space as possible and to get out of the way and not draw attention to themselves. When you drive a lorry, you take up a lot of space, often can’t get out of the way and draw attention to yourself. So you have to go against your instincts. Once I learned to do that my confidence grew and I now perform 3 point turns in junctions left right and centre. Before, I would have driven 8 miles to the next roundabout to turn around (exaggeration, but you probably know what I mean).
Another element of confidence building was my approach to reversing. Basically, I learned to embrace it and not dread it. Accept that more often than not you will have to reverse into a drop. See every opportunity to reverse as an opportunity to learn and improve. Eventually it ALL feels right and clicks into place instead of just one or two parts of it doing that. I’m getting towards that point but I’m not quite there yet.
Example: Due to the nature of my jobs, I had never reversed onto a bay until last week, when I had to do it twice. One was in a farmyard with one bay. My first approach was slightly off and I didn’t have enough enough space to straighten up. So I pulled forward to try again and someone came out and helpfully told me to line my left mirror up with a join in the yard paving, which would get me onto the bay. I pulled forward a bit more and proceeded to line my right mirror up with the join, giving me a perfect view of the bay in my right mirror 
So I did a good reverse, just not in the right place! Third time lucky. I was able to laugh it off instead of agonise over it, but only because as my confidence has grown my imposter syndrome has diminished. Get used to assessing your own reverses: was the set up not quite right, did you turn too early, did you not pull far forward enough, did you mix up your right and left 
or did you nail it?
As well as looking out for natural guidelines like lines in paving which sometimes are obvious and sometimes you don’t see until you GOAL, or someone points them out, other things I have learned have mostly already been mentioned. Don’t be afraid to use all the space available as that enables you to set up with a good angle and get that back wheel as close as you can to where you want it to go without having to deal with sharp angles.
Reversing around a corner is easy to oversteer - it’s less one big turn and straighten up and more turn a bit, straighten up a bit, repeat. Watch your back wheel. Use markers on your lorry (curtain straps, mudguards) and draw invisible lines to the ground to learn where the back of your lorry actually is. How many times have I got out the lorry to look only to find I have 5m in hand instead of the 5mm I thought. Then I have a good look in my mirrors to understand what I am actually seeing and why it looks like 5mm but is actually 5m. You can watch videos but nothing will substitute for practice.
You didn’t say what kind of driving you do, but I find finding places for the first time and getting in and out of them takes up a lot of energy. It makes such a huge difference when you know where you are going and what you are going to do when you get there. Something I should have added to my previous post is don’t be so hard on yourself - another thing women often grow up doing and it’s a hard habit to break because it’s so subconscious.
