Grades are not important, knowledge is
I heard 90% of people with Bachelor's degree don't have work that matches their education...
so just switch to professional middle school right away, and look for free courses/ study groups that might even pay you for the fact you attend...

I wasted too much time learning about culture and literature nonsense, when all I ever wanted was basic math, web design, info about how world economics work and how to live of my own garden...