You can either go forward with biology and chemistry or you cna go back. from what you say you are not likely to do well in either and or you will hate doing them.
If you want to do law , then grades matter, subjects are mostly irrelevant. If you dont get the grades, then it will make things more difficult for you in future.
Your alternative is to go back and repeat the year, do A levels you enjoy, get good grades and get on a good law course. Its not so bad repeating a year. You might wnat to rethink your epq or make it relevamnt to law.
Unfortunately its time for you to make a decision on what you want. As you said you dont wnat to repeat, dount many people do and a year might seem like the end of the world. That said it goes quickly and id mucch rather spend an extra year rather than risk not getting to do what I wanted at all.
I would do the year again without hesitation, but its your life and your choice. I might rethink if I knew I was going to get a good grade in bio and chem.