Hope you enjoyed the trip.
It will get easier with time. You still have tomorrow to practice and get used to it. Us Brits have the same problem with touring in most foreign countries, and PBP. The time it's most likely to go wrong is when you think you've got it. I had that problem in France when I was touring a few years ago - switched off and turned left at a junction onto the wrong side of the road, and then had to pull over straight away as there was a car coming.
Here in Cambridge we get a lot of foreign students and they are notorious for riding on the wrong side of the road. One colleague years ago was going around a roundabout on his bike and was confronted by about 30 bikes coming the wrong way.
On LEL, follow people with Audax UK tops, and do what they do.