The potential change from 8th grade to 9th grade is insane.
Some kids mature early and dominate in middle school, and still others actually have a big training "program" in middle school which allows them to beat the kids who only run 2 miles a day (lots of middle school programs do that).
I know a middle school kid who was the best CC runner on his team and killed everyone else. When he got to high school he didn't really improve and ended up being a 19s guy. One of the guys on his middle school team that he used to destroy got down into the 15:30s.
I know another middle school kid who ran 12:10 for 2 miles in CC as an 8th grader and by indoor track of his freshman year got down to 9:55 for 3200.
You just can't tell what the progress will be. Still others improve a lot after high school even.
So, will the OP become a good HS 800m runner? Only time and training will tell.