Well done you for trying it out only 5 days in!
I waited several weeks because I was so nervous, and my first time was... Um... Sub-optimal.
I agree that overcoming all that learned muscle memory from US driving on the other side is a factor. I was pretty good at trying to shift the door when I was first learning.
Add on top the unfamiliar road signs and there's just so much to pay attention to all at once. On my second try, I was so concerned about recognising and obeying the road signs that I arranged a rather unfortunate encounter between DH's car and a hedge. To this day, the scar of that meeting is still visible on the blue paint.
I highly recommend lessons. I can't recommend them enough. Generally, I don't think family and friends are the greatest choices for driving instructors. I found there was always that niggling bit of me worried I would accidentally FUBAR my spouse's car, and that worry really interfered with me being able to allow myself to learn and make mistakes. An instructor will not only have a second set of controls, so it's highly unlikely the car would veer or bump into anything, but insurance specially to cover having the car being driven by learner drivers.
Plus, a lot of the exam isn't really about being able to drive, but being able to drive a certain way. An instructor will know exactly what will be required, and most likely, will need to help you break a few pesky bad driving habits from the US that would be marked against you.