Ivan man, I get it. I'm very much the same. Even when I decided to enter a tournament more than a month prior the nerves and anxiety really kicked in for the next few days haha, and I hadn't even entered yet!
Your mindset is really important regarding it all. Of course I know you want to do well, and don't want to lower your expectations of yourself etc, but it's important to not have it as an overarching looming all-or-nothing pressure.
You've done all the training you could, now you can relax and just do your thing. Let your training speak. You can relax now in a way and just honestly have fun on the day. Seeing the comp as a learning experience and a way to become better takes it away from it being a high-stakes thing and into a more curious process where you explore what you're capable of. And again, this isn't a diminishing of your goals to win, even when I compete with a more open (less rigid) attitude I still would like to do well. But moreso I'd like to be proud of how I perform regardless of result. So I still try my absolute best, but the sharp edge is taken off on having to win and it being a reflection of my self-worth and value. I compete as I love doing my favourite thing in the world in a place outside the confines my own dojo, out of my comfort zone, finding new ways to learn and grow in my MA and as a martial artist, and to enjoy the amazing comradery and MA community.
What/how you do is not the most important thing to me, but who/how you ARE is. Carry yourself with dignity, respect, and the fact that you're entering is already a massive win. It already speaks worlds about you. Let who you are dictate your approach, and not let the hypothetical result dictate how you feel about yourself, you know?
Always recommend to connect deeply with your breath. Slow your breathing by bringing it down into lower stomach, but letting it expand your whole body in 360°. Let it deepen naturally without force, and it helps regulate things. Breath is a really, really good anchor and stabilising balm, mentally and physically.
@Monkey Turned Wolf's suggestion is also spot on. Doing a form or slow MA movements can really help you unstick and get out of your head. Shake out your shoulders, breathe out your tension and connect to the ground. Moving around in a fluid relaxed way helps to remind you to be more relaxed and fluid physically and also with your thought life and mindset.
Regarding your direct feelings of anxiety, almost treat it like an old friend who comes along with you. And by that I don't mean indulging in all the thoughts and 'what ifs' etc, but staying with the feeling. Keep your attention on the very core of the feeling/sensation itself. Be with it, totally. Is it located anywhere? Is it more diffuse? Just gently rest your attention on the very feeling and be with it without trying to manipulate it in any way whatsoever. Explore it with an attitude of openness and curiosity. When you try and approach with force and control it can often create more internal division and conflict. An attitude of curiosity is powerful and gentler, but very effective in unravelling things. Note: a curiosity that's light, and playful, rather than one with intensity and furrowed brows

. See what happens when you just allow the feeling to be there. Seeing it without any judgement whatsoever and giving it space, in which you are being the space for it to be. It's just an ooooold friend, that's okay. It can be there.
Take your stoicism application to the next level. So there is stress there. Stoicism isn't about getting rid of the stress, because that's also another form of control. Reality is, it's there. You didn't decide to bring the stress there, why would anyone? So let go of controlling it, see what happens.
Realise the anxiety may be there, it may not. It may come and go in waves. But it doesn't have to affect you. Just do your thing, be yourself, express yourself authentically out there on the mats, and mostly mate, enjoy the comp
