did ok in my mocks but messed up the real thing…i’m at a loss

i transferred from the hong kong education system to the uk one in y9 (f3 in hk, because hk is a year behind) so i’m already a year older than everyone else in my year. it was never a problem for me before because we were pretty much on the same level of everything and i didn’t do bad in school. i’m currently in year 12 and i’ve just flunked my external AS exams (CCD) even though i did decent on the mocks earlier this year (AAB). before those exams my predicted grades were standing at a solid A*A*B. i study english lit, spanish and economics and i want to apply for a joined honours law and spanish law course.i asked to repeat a year because i’m not confident that i can turn everything around in less than a year before uni but i can’t because of student visa complications since im already 18. my examinations counsellor also advises against repeating a year somewhere else even though i honestly don’t even care if i end up graduating at 20. what should i do?