I would avoid leaving school if im honest. It's fully your choice of course but why exaclty did you choose to attend an academic institution if you are not commited to attending? If you are only doing this because "it would be a waste of time to give up now" then you need to re-think your plans for the future. I think it's a very very long shot that your college will grant you permission to do this. I mean not to come across as rude but you have no real reason apart from lazyness. I would stay in school and attend your lessons but work hard every hour you are free.
Many people say they could quite college, work from home, and get top grades but whilst it seems feasable and is, you are underestimating it. I have seen people do what you are planning on doing and It is not an easy ride. You should be fine if you are very inclined toward academic acheivment. If not, then stay in college, work hard, and you will do well.
I just read you OP again and you mention that not attending college would give you more time for external employment? If you are planning on working half way decent hours in a job on the lead up to retakes whilst self teaching then prepare to fail.