All we can do is what we can. Take a deep breath, take a step back, and know that you have done well to prepare you for this point. Do the same things you have been doing to prepare and you will be able to get through this. Trust that.

It is the stress that gets to us at this point and it is important to take some time to do what you need to let it go, for everyone it is different; find that activity that you can distract from things and relax for a bit: whether it be listening to music, watch a movie, exercise, take a nap or hot bath/shower, go out with friends or just get in touch with them, but something to unwind, then come back to to your studies. Take more frequent breaks too; you need more mental breaks from it, then come back to it.

You are almost most there and it will be over soon. Hang in there and do what you need to to take care of you.