Wow. Coming from someone with an Autism Spectrum Disorder, your parents need to chill. As long as you are doing your best, there is no reason for your parents to ground you. Explain to them that you are doing your best, and there is nothing you can do better at the moment.
Sometimes a subject doesn't come naturally. In that situation, do your best, and be thankful for what comes from it. I got 2 D's in college Chemistry. Did I do my best? Yes. Am I proud of my D, yes. Did I switch majors in order to study something I am better at? Yes. Lol ol.
Long story short, do what you do, and do it as well as you can. Be proud of your skill, no matter what level, because it is your best.
Sorry for the rant. :P