Frankly it sounds like you need a different instructor. Not all are equal and for more nervous drivers specialised ones are necessary
I was absolutely getting nowhere with my 1st instructor who only ever criticised and never guided and couldn't understand how to work with me as a pupil, attempted first test under her and was failed for lack of confidence/hesitancy!
My 2nd instructor worked WITH my anxiety and overthinking and within a few weeks with him it "clicked" he took the approach of "making a virtue out of a vice" so instead of vaguely and in an unguided way me overthinking he channeled it into applying it to what I was doing - so eg changing gears he'd explain to me what was going on in the car when I did that and why it was necessary and I was then able to use that information to learn and overthink "mindfully" sort of
Worked a treat! Passed my second test no problem
I have to say I also agree lessons alone is not enough practice you need to be driving as much as possible
My ex used to take me out driving as much as possible, we'd also do things like go to the empty car parks of a weekend on the army base where we lived and practice the manoeuvres too he'd even chalk out "road markings" for me to practice these, we'd use nearby items (cones not being used, bins etc) to place as representing cars I had to park between etc
Helped a lot
There's also an old learning to drive adage :
As a learner you learn to pass the test, once you've passed the test THEN you learn to drive!
It's a shame you have nobody you can do this with - is there really nobody?
Is there not even anyone who would drive you to an unused area you can practice in without them in the car? You only need someone in the car on public roads