I do not want to belittle your frustrations. But by defintion half of all the people are below average intelligence, doesn't mean they're doomed to unhappy unsuccesful lives. Intelligence is an ill defined, and overvalued concept. You seem reluctant to continue your education, that means that education is probably a bad idea for you now. If you're not motivated to receive education, it won't stick. And education (in one form or another) will always be there if you choose to pursue it.
I would strongly encourage you to seek opportunities for learning though. Those can be from practical one-the-job opportunities, or pursued in your free time. Find something you're excited to learn about (doesn't matter what it is), and learn about it. Train your brain in processing new information and ideas. And never allow yourself to doubt your ability to do so.