Help with microsoft word 2007?

i have an essay due tomorrow and it keeps underlining everything in red! and i spelled it write! for ex. if i write anybody it underlines it red. if i write evaluative it underlines it wrong! but if i write just one letter such as a, x, c, etc. it doesnt underline it. how can i know im spelling the words right? it has to be a long essay, and im not the BEST speller, and i dont really have time to read it over and over. im also a fast typer! and im only 11. please help! i also dont understand what could be wrong! its a 2007 version!