I am going through a similar predicament.
Doing the IB here. But maybe some parallels can be drawn.
HLs: Math AA, Physics and Business Mgmt
SLs: Eng A L&L, French B and CS
Going to start Y13 in September.
Due to endless and a litany of social and personal problems that contributed to very high stress levels along with health problems, I lost focus in life and I ended up scoring 5s in all my subjects for the mocks. But it is never too late.
Although my stuff is gradually being sorted (or so do I believe), my grades took a massive hit, and so did my focus, my happiness and health. But now I am slowly rebuilding, and I have made a commitment. I want to get into that (my choice) college, and I won't stop working hard with conviction and dedication until I do.
Besides there is something that matters even more than grades, and that is your personality. If you show that despite getting not the best grades you have not given up, that is a big, big plus. Believe me.
But yes, Ghostlady is right. Not everyone does their best in Y12 mocks. But you need to bounce back before the next mock session, and be the person that everyone will look up to in academics.
Do not lose hope. Maintain a discipline and follow it with conviction.
You will get into your dream college.