Don't worry about being in a school with a lot of students. I've spent my whole school life in a school with 2,000 other kids around, and it's really nothing special. The only difference is that you won't know everyone in the school.
And even though I'm a grade above you I won't actually be going to a high school until next year because my district has this weird set up where ninth grade is in the jr. high school instead of the high school, so I'm not really sure what to think of this.