That's definitely ambitious to try for Juilliard.
Congrats on the Rachmaninov Prelude! I played that about a year ago.
Anyways, these may not be the exact pieces you would use for the audition, but just to get started with the feel of the types of pieces, and as you progress, you could replace these suggestions with more difficult works:
Prelude and Fugue No. 2 in C minor, BWV 847
Sonata No. 50 in D Major by Haydn
Prelude in B Minor, Op. 32 No. 10 by Rachmaninov
Impromptu in E Flat Major, Op. 90 No. 2
Skip the Etudes for right now, unless if you really wanna play Chopin's Op. 10 No. 3 or something.
Maybe the Shostakovich Fantastic Dances Op. 5, maybe the second movement of Ravel's Sonatine.
Again, these are only preparatory and
could work for an audition, but harder pieces would probably suffice. Good luck! I'm an eighth grader too