Please help

Is there something you really enjoy doing that might help get your mind off it, if so take a break for today, do that. and for the rest of the days, try to study in short (30-45 min sessions) with plenty of 2-5 min breaks between them, and then set yourself some small goals for each day and when you complete it, reward yourself with something, like a couple of matches of something, or some food you like, or a stroll through the park or whatever floats your boat.

also there's a piece of advice I was once given and that stuck with me: To study, the best is on a full stomach and empty balls

ive been there.
first of all. you need to cool down. relax.
the past is the past. you can only do so much. concentrate on the future.
my father always told me this when i panic'd the day before exams
Why are you so nervous? Didnt you learn enough for your test? Because if you feel like you did enough, you have nothing to worry about. Trust in your abilities. I know you can do it.
And i know you can do it too. Be confident. Learn to believe in yourself. Just tell yourself you can do it.

What kind of test are we talking about? What is the name of the teat? A final exam? A university entry test?

Hey, I feel for you as i use to have the same kind of anxiety when i was at the university, until I finally realised what is done is done, and can't be changed. What you have power over however is the future tests, so focus on that instead.

Just try to take deep breath and calm down if you're feeling the anxiety pressure your chest... and look at it objectively. Sure one exam went bad. So it happens. It's life. Doesn't mean your whole life is over. Yesterday's exam is gone and you're done with it, flunked or not, it's over. Now you're lucky and have a chance to do good at the other part, great! So focus on it instead.

Also, for the future, if it happens again (eventually it will, maybe one day you'll have the flu, or they will ask an obscure question that wasn't in the material...), remind yourself that it's what it is, "just" an exam and it won't define your whole life even if at that moment it looks like it. Believe me, the day you'll get out of the uni with your diploma and after that, you won't even remember the few exams you did bad at, and nobody else will either ;)

And good luck for your next test. Remember as long as you do the best you can and you know you have studied your topic, there is no reason to overstress yourself ;)