Grades really aren't worth worrying about. If your parents are more worried about your grades that your mental health, then they need an intervention.
Not achieving grades isn't the end of the world, I know it can suck, because I failed a fair few that I thought I passed. I ended up leaving school with one higher at a D...That was in RMPS neehoo, I went on to get a job for a few years, went to college, and now I'm away to do my degree.
You can't go back and change what you wrote in your paper, if it ends up that you need to resit, then resit, if you have to end up going to college, then go. My main concern is that you think your parents won't support you whatever your grades are. They love you unconditionally, and will support you in whatever way you need it. Speak to them about your concerns and see what they say. If they go mental like you suspect they do, then refer them to "how to love your child after exam results day 101"! (sorry for the sarcasm there, it's a bad habit I have!)
All they can expect is that you went into your exam, and did what you could. Do not worry yourself sick about this, because in the big bad world, your grades really don't matter, the only thing they do is determine how much tax you'll pay in your career! :P
In all seriousness though, exams while they are stressful, and waiting for results is rubbish, do not get yourself worked up about it, try as best you can to put it to the back of your mind until results day, and DO NOT try to look up answers to your paper.
Then take each step as it comes about your future, who knows, maybe you've done better than you think!