Are you sure 8th grade courses go into your HS GPA? This would be way out of the ordinary. You may want to get a source more authoritative than a friend’s brother. At our school, they go on your transcript but are not calculated in. Our policy is documented in a student handbook - doesn’t your school have the calculations documented somewhere?
But either way, as noted above, it’s, at worst, one of 30+ courses with grades that will factor into a GPA. And it’s in the past.