Practicing an instrument alone is humbling because nobody covers your wrong notes. That’s exactly why it works.

Playing alongside other people lets your mistakes get absorbed by their sound, which is comfortable and slows you down. Alone, every wrong note is attributable and audible, and there is nobody to hide behind or blame. That is unpleasant for a week and then becomes the fastest feedback you will get, since nothing is smoothed over.

Take the four bars you keep fudging and work only on those, slowly enough to get them right. Speed hides errors, so slow practice is the honest kind. Fifteen minutes of that beats an hour of playing the parts you already have.