The personal statement is also a great place to explain more serious problems, like less_than_ideal grades or test scores. Don't be afraid to write something like, "I don't test well" in the statement. As long as you can provide a good reason for you app's problems, it's okay to address them directly. You won't be able to hide it from admissions officers anyway, so providing a reason for problems is always preferable to ignoring them.
When you are trying to get into a university, a grad school, or even a specialty school, more times than not a personal statement is required. The first thing that you need to do before you begin to write your personal statement is to write down all of your thoughts. After that is done you can begin to edit your work. You may want to believe that your first thoughts are gold, but in order to write a successful personal statement you must edit it often.