Great job on putting in the effort here! I agree with John that, in your situation, the best way to improve is to seek out external advice from "someone who's done this before". Examples including reaching out to friends/alumni working in consulting and hiring case experts online for a mock case. Nothing much to add here.
However, if you lack such resources and are hesitant to hire an expert online, the best way to further improve may be doing and recording a case, listening to it and critiquing it from the perspective of a case interviewer. You should be able to find online what interviewers are looking for in a case. Of course, this is a compromise solution, and may not be as effective.
Feel free to message me if you would like to discuss further.