ARGH !!!I`M SO DUMB!!!what do i do now ?

well,stupidly , i decided o play rachmaninov `s prelude in g minor op 23 no 5 for the concert. not a big deal, a yearly event in the academy. i`m in grade 4 , and not very experienced , and no child prodigy either. there`s one week left , and i made this decision just yesterday , so today when i started to practice , obviously i sucked !! i know it`s stupid of me . Rachmaninoff`s an incredibly difficult composer . so , my question is do you think i should give up trying to play it and play something easier like . or should i work extra hard at this piece and try to get it done ?if you play piano , you`d know how tough this is . what do i do ? suggest some alternative pieces , vivace , if possible . should i get ahead with this or let it go >?