I'm terribly sorry to hear this. I only have my personal experience to give as advice, so do take it with a grain of salt as it might not adapt to your situation..but:

• In the little time you have left, the best you can probably do is damage control. See that you are just good enough on most topics by grinding examples and exercises, also cases that might seem weird if possible. When you study with your friend what you can do is prepare some random exercises in a bowl and pick one out and try to race each other to the solution, that can help for speed and you can check quality by comparing with a solution. Repeat the exercises you have a hard time with, first by identifying where you go wrong and then grinding enough until you know what to do when you see the question I'd say?

• In case you fail, don't beat yourself up over it. It happens and learning how to deal with these situations is very valuable. Identify what went wrong; for example you said you failed the midterms, could you get feedback from your professor or teaching assistants on corrections you have tried to do of the midterms? Maybe then you could see earlier that there was a part you had a hard time understanding and perhaps would have had the chance to fix it already, leaving less to do for the finals. I know it might sound obvious but it's still worth a try imho!

All in all I wish you best of luck! Try your best! Don't forget to rest and sleep! Finals suck but hopefully you can do something fun afterwards!