Meg Hey Meg,
I feel like at this point dropping a subject is really not worth it as you have already done the content for most of them. I also 12 unites and many of the same subjects (english adv, maths adv, modern, sor2, legal, history ext, english ext) and although I also want to drop maths at the moment, you may as well do the exam just as a backup in case you crash out in one of the other exams