I made bad decisions and ended up in a B in Chem. However, I got As both semesters of Bio last year. Should I move up my Bio grades so I can save my 4.0 gpa?
Once you get less than an A, your 4.0 is gone forever, Whether your 8th grade bio grades will count towards your HS GPA is a matter of school policy. If the school gives an option, then sure, have them count. If the school does not allow the option, you will not get policy changed in all likelihood. Regardless, one B is not the end of the world.
The important thing is to know why you got a B and what you could do differently next time.