you need to take a deep breath - because unfortunately there's nothing that you can do about it now. there is no point in worrying and panicking, and i know that feels like the most impossible thing right now, but just park it for now. you can worry about all that in a few weeks - or better yet, just don't worry about it at all.
the best thing you can do right now is be kind to yourself. forgive yourself. and know that you can always resit it if it's so awful - but for right now, take a break. you've worked hard and im really proud of you, but if you're tired and stressed and overworked then you won't do as well as you can on future exams.
put it all to the back of your mind - there will be time for that later. visualise yourself locking those feelings away, because it's not important right now.
grades aren't the only important thing in the world - or even one of the more important things in the world. just do your best, because at the end of the day, that's all you can do.
i wish you the best of luck darling - sending positive vibes to you xx