I understand your position. Are you doing JC or pre-u? Since you have done 2yrs, why not just suck it all up and do what we call a total mugging stint, pia all the way. You have to mentally prepare youself, and really give up whatever bad habits, just for one whole year.
Whatever school you are in, go and look for the teacher with the best influence on you, have a good talk about your situation. Get advise and support. Have a good talk with your parents too, see if they can help you by giving or loaning you money to get private tuitions with your weak subjects.
I never had such guidiance before, and I was pretty alone when I was in your position (finish 1st year - pre-u, retain). I made my choice to jump to poly, which was no better in terms of study enviornment (did 4yrs for 3yrs course). It pretty affected my personal outlook, but I slug it out during poly, and by hook or crook, scrap a passing grade in the end. Almost got kicked by one of the retaining course.
Don't take it too badly in any case, you are still very young, think clearly on your path to take. Low education does not mean cannot make it. I haven't got a chance to use that diploma paper of my yet, I am still slugging it out every single day on my own 2 feet, for the past 10+yrs already, don't need the paper. But good to have something to fall back on.