I work in machine learning and I don't think a 3 months course is going to transform you in a machine learning engineer. I think you need at least the time you took. You need to learn the maths, statistics, etc. Apply those tools to real problems, get some experience with different problems and techniques. And, finally, be involved in some type of research. Because machine learning is evolving so fast, you need to learn how to read a paper, how to understand it, and how to apply it to your problem. I see no way to do everything it in 3 months. You need at least a couple of years and be lucky to find a job related, so you put your first step in the industry.
And congratulations for you achievement and your bravery to quit the job!
And congratulations for you achievement and your bravery to quit the job!