Apologies for the long answer, but this is a situation I found myself in Year 12 but managed to remedy for Yr13.
As you're aware yourself it seems, you haven't put your self in the best position. The honest truth is just becuase A-levels are so intense you can't change that on such short notice. I would recommend that you try and relax yourself and much as possible now, put yourself in the "You have nothing to lose and everything to gain" mindset. The more relaxed you are the better you will likely focus on what ever content you can recall and apply.
The long term fix for this is also something you have identified, seek help from a professional. They will help you ! that's why they are professionals. Rest assured They won't turn you down becuase of other peoples needs, they are there to and will always help. As for feeling the pressure of A-levels that is completely normal, everyone from your year group is nervous/anxious or scared to some degree. That being said if you feel that this pressure is disrupting major aspects of your life such as eating, sleeping and social interactions then it may be time to speak to people around you as well as professionals.
My advise for right now is to acknowledge the pressure, it's there it won't go and won't leave until you open the envelope in august. It is EXTREMELY difficult to just clear pressure off your shoulders, very few people can genuinely do that.
That being said you can do things to minimise its effect on you.
1) You can understand you have a limit, you can only do so much with the tools and resources available to you.
2) You aren't made of metal, you will feel the pressure and it's COMPLETELY normal.
3) The limited spare time you have during exam season, try and make it extra fun, do things you actually enjoy and something that switches you off from school.
Also academically, all hope is still not lost you can still do some things to ever so slightly improve your situation.
As you are tight on time I would recommend, identifying the highest yield topics for each subject and then do past paper questions for YOUR weakest high yield topics. I wouldn't bother with specific learning or recall like flashcards, this close to/in exams I would be doing past paper Q's only and checking mark schemes thoroughly.
I am sorry you found yourself in this position, I know from experience it happens a lot faster than you account for.
Listen, Whatever happens you will learn from this whole ordeal. You will learn how to cope and deal with pressure much better.
Just do the best you can, becuase truthfully that's all you can do.
Good Luck !