Those diversity statements are tough. I know mine sounded like I was trying too hard, but I was at a loss of how to come across more genuine.
As for motivation - read a bit of one of your favorite pieces of historical literature to reinforce why you love your field/topic and then put on some headphones and listen to anything that inspires you to write (atmospheric, classical, indie, whatever). If you're brave, add a glass of wine. It can help you relax and stimulate the ideas to flow.
I'd set a couple alerts on your calendar and plan to send maybe 2 more reminders in the coming weeks, and then if you still need to, the day before the deadline.
Having a plan might keep you from freaking out..hopefully