I've read incredibly long essays that say very little and therefore they get very low marks. I've read short essays, sometimes much shorter than what was assigned, that had phenomenal things to say and therefore they received high marks.
Content is important .
Better yet, make up an outline. Nearly every student who does this will end up getting a better mark, guaranteed. Make a rough draft. Check out all those things you underlined or starred. Read the essay out loud to see what flows and what doesn't flow.