One month of solid revision for GCSEs is plenty of time. If you work hard you can still ace everything. Focus, set manageable goals and work a couple of hours every day and you'll do brilliantly.
This thread has reminded me of my chemistry mock result in year 11, I got 4/100 and my teacher basically told me I was an embarrassment.
I got 100% in the exam. Just shows you anything's possible with a bit of work! Good luck to you all! (Though I'm sure exams are probably half way to nearly done now.)