hifirst of all, don't be too worried and stressed. I do math physics and biology and last year in my year 12, I missed a lot of school for sports, I was behind with content and obviously, in the end, I didn't do too well. But I changed my mindset this year into balancing what I enjoy, sports, and studying a reasonable amount of time. its taken me exactly 5 months, from December 2018 to April 2019 with serious commitment and a little help from friends in the three subjects to turn D's to B's and hopefully A's in the final. what I'm mainly trying to say is it's okay to re-sit as long as you work hard. Nothing good comes easy and if you just plan your time wisely, you can work miracles. For the time you have left this year, cram content, sit your papers and before that, explain to your parents your situation and that you will improve next year. Work hard from day 1 and slowly you'll see yourself doing better!!