How do I stop being so mentally handicapped??

So basically, I went to a trades school. The hardest thing we reached was at 6th year (17 year old) with Integrals, basically calculus I. The thing is, I have been dragging the mathematic exams since 3rd year ( 14 years old), and I haven't finished school yet, exactly over 6th year mathematics. I'm 19, I enrolled in mechanical engineering, and the uni only waits for me until the last week of july to show up with all the papers. I have been studying, obviously for calculus, I can solve all the things, but I get lost with all the theory; not to mention that I really struggle to make one advancement with algebra, exactly with anything harder than adding or subtracting matrices. I really want to stop this sort of mental blockage but I can't really find a way to see this as a tool (because not even in a thousand years I will like this) and not a toll that I have to pay.

Pd: Changing of career is a complete NO