I ran into a similar problem (maybe, in a way?) when I mistakenly carefully crafted a 500-word essay instead of a 500 character statement (whoops!). i called the admissions office in a panic and they said to submit it anyway, though they wouldn't guarantee that anyone would read it. i made sure to verify that it wouldn't count against me; i wasn't trying to suck up, but after spending two+ months on the essay, i didn't want to just throw it away either. because of extenuating circumstances which i included in the essay, the person i spoke with said it was OK to include it.
i know it was somewhat careless of me not to notice the specific instructions. in my defense, i had been working on the application since the previous summer, and hadn't looked at the school's admissions FAQ's since then; it was between that time and now that they updated their website to clearly specify that it should be a short statement rather than an essay. my guess is that i'm not the first person to have made the mistake.
anyway, the lesson learned is to follow instructions as best as possible, but if in doubt, it doesn't hurt to call the admissions office and ask.