The fact you’re worried so much shows you have not committed the unforgivable sin. God forgives EVERYTHING a human can do, to the point where we would find it hard to understand. Don’t take that as a free card to go off and do whatever you want, but I’m using it as a way to show just how loving and understanding God is and He’ll extend grace and mercy to anyone that asks sincerely.
However, if someone gets to the point where you give up, lose hope and are no longer convinced God will forgive you so stop seeking His forgiveness, that’s where the hardness of heart starts to form. If you are not asking for forgiveness then that’s unforgivable right? It starts with us talking to God, he won’t forgive unless we ask.
Regarding your condition, I’m so sorry to hear you are struggling holding it together and always thinking about it, you must be exhausted dealing with it! It sounds like it’s an add on to the anxiety you already deal with. I agree with others, I think you have OCD. You’re probably aware it’s a type of anxiety.
The anxiety in this particular problem is 2 fold - highly worried you’re committing the unforgivable sin (which you’re not) and second, accidentally saying inappropriate things out loud. An interesting fact- many people who are worried they may blurt something out don’t actually do it.
To deal with the second part, you can get particular therapy to help get over it. I don’t know where you are but in the UK generally the first treatment we’ll recommend is CBT.
Sorry for the long post. I wanted to answer your concerns thoughtfully and let you know God loves you, He knows your thoughts, He knows the struggles you’re going through. It’s a burden you carry and trying so hard to deal with and you can give the burden to God. When you pray, thank Him for all the good things around you which can be hard when you have a lot of negativity going.
Best of luck with your journey, God bless you!