I got 866555544 at GCSE and taking a level psychology, sociology and French (+EPQ). I feel like my GCSE grades are bringing me down
Do not worry at all, most universities for Law only ask for a 5 in maths and English Language sometimes (rarely) they may ask for a 6 but other than that you should be fine. I have lot's of friends who got lower grades and got offers for Law! just focus on your a levels as they are more important.
Stop worrying about your GCSEs - that ship has sailed. Its your A level grades that matter for Uni entrance. Pick three A level subjects you will enjoy studying and work hard and you'll be fine.