It's too informal. Don't be too stiff but, at the same time, don't get too loose. The voice you use in your essays should sound professional but, at the same time, it should be a little informal. Try to imagine the voice you would use if you were interviewing at the school. You also don't want to sound chatty or use a lot of slang.
Most schools are pretty serious about their assigned essay lengths.
You can exceed the limits by 50 words or so, but 100 words is pushing it. That's especially true at Harvard, where the essays are very short. And if you have to, then be brief. The optional essay is not a forum for you to unload all of your insecurities about applying to B-school. If you are going to use it to explain sub-par grades, don't whine or make excuses.