Best model to help to keep system in line

A self-taught amateur AI developer is struggling to manage a 1,200-line Python script for an AI assistant and seeks advice on maintaining control as the project grows.

I have been working on an AI assistant for a long time, and have tried many times to find a system for it to run on. I am a self-taught amateur, but have come a long way so far. My question is how do I keep track of it all, because it has grown to over 1200 lines of script, and is far from finished, how do I still manage to be the leader and have control of the entire design with all the codes for tools and other things? I am facing an imminent division of the Python file. I can feel it starting to slip out of my hands now. What is the best thing to do now?