Contrary to what lunar mike wrote, please don't rely on (a) god(s) for your problems.
Anyways, I'm not taking the entrance exams in Japanese, but I understand how you feel. It seems like my professor in rushing me. Since the first week in Japan, he has treated me as a Masters course student, even though I am actually just a research student. Also, I don't have experience that the masters course students have. So when our monthly research reports comes around... my report is quite short compared to the other students. Plus, my results up till now has rarely been good and I have done nothing significant. My undergraduate major is a bit different from what I am in now, so my knowledge of the field is not very good right now. So yeah, I feel a bit depressed to.
But hey, being depress and sulking about it will only slow you down. Please continue to work hard and move forward. It's okay to fall, just be sure to get back up and learn from your mistakes.
If you feel like you are not ready, you can always wait and try the entrance exam again next year. You have plenty of time I think. Make good use of it.