A popular saying is that the key to success is to start before you are ready. The basic idea is that one can never really be fully ready so one should just get started and learn along the way.
For example, if you want to learn to be a good competitor, you should just dive in and compete even if you are not ready. The experiences you will gain in the competition will help you improve and become a better fighter.
The more you do of this, despite not being fully ready, the better you become. And over time, you will become a good fighter. All because you started competing straight away and did not wait and wait and wait until you were ready (which would have been never).
No matter how much training, drilling or mental preparation you do, you can never be ready for competition. You could train for years and you still won't be ready for competition. You learn how to fight competitions by fighting competitions.
Now, this is not to say one cannot be prepared. There is a huge difference between being ready and being prepared. If you train hard for a certain amount of time, you could be well-prepared for a competition (you just won't be ready for it, precisely because of your lack of experience).
Imagine you have a competition coming up in six months and during those six months, you trained practically every day. You do your HIIT and strength training, you do gripping training, you practice throws and groundwork, you do situational drills, you do randori and you do mock shiai. And you do this for half a year.
Will you be prepared for a competition six months after you started training hard for it? Heck, yes. But will you be ready? Hell, no.
You will be prepared in the sense that you are fit and strong and you know all the things you need to know about standing and groundwork. But, having not had any competition experience, you will be nervous like crazy, almost to the point that it might debilitate you. You woll not be used to the pressures of competition and this too will negatively impact your ability to fight to the best of your capabilities.
Remember: You will never feel ready for your first competition. But you can be well-prepared. And if you are, that's all you need. Go into the competition well-prepared and, win or lose, you will still have a good learning experience.