One Section with multiple Google Classrooms

I teach 6, 7, and 8th grades in Middle School and teach each student 3 times. I create a new Section when they are in 6th grade, then simply change the curriculum, name, and grade level each year. Students only have my class for a 9 week period, so I add more kids every new term. There are between 200 and 300 students in each Section. In past years, I’ve had student click on the link I post to join the section. Then they create their account and reuse the same one year after year.

How can I do this with Google Classroom signups? I made my brand new Section for my 6th graders then picked Google Classroom to add my roster. No issues…but that was just one of my two periods of 6th graders. I can’t figure out how to add my 2nd period class to the Section. Each period has its own Google Classroom.

Any thoughts?