Bear with me with this non musical analogy:
I am a driving instructor and one of the things we look for is for a pupil to know they can drive by themselves.
One of the questions they will eventually ask is: “how do I know I am ready to drive by myself?”
My answer is with this question: “ when you drive, how do you feel?”
The answer we look for is: “ I feel I don’t know anything, yet I can still do it!”
That’s when I know that the skill has become theirs for life.
Back to piano playing.
I have studied classical artists from different eras and memorised several compositions which led me to being capable of improvising in those eras or artists.
I’d say I am a fairly skilled pianist......
I don’t feel I am in full control when I am playing an artist composition. In fact, it can be great one day and bad on another.... it’s not really bad but enough for me to make mistakes.
I practise these pieces regularly at different speed as well as practising different phrases which I can use when I improvise.
Mistakes or flubs do not happen when I improvise.
I have been playing for about 6 years.
I know these pieces well. I always play from my brain and not my fingers but sometimes I get “distracted”.
I’ve been thinking I cannot “perform” pieces. Maybe? Hence the problem?
PS: I recently started to work on jazz studies and I have very few problems, if any?!?
EDIT: I know my technique is fine. This seems to be psychological when I play pieces. All my scales and chord are very good too. In fact, I have spent a lot of time practicing these.... and not played as much music... Could there be a gap between the two?