You should be honest with your parents about how you have been struggling with school and GCSEs so that they'll be able to find extra support for you, such as a tutor. It would also be a good idea to resit them since a lot of A level courses build off of knowledge from your previous exams. It really is never too late to turn your life around and improve areas that you've previously neglected, like it's been said, you really will end up surprising yourself. I'm sure everything will turn out to be alright as long as you try, good luck though!