@HollySchneider ...
Ugh! Sorry to read that you had to do the assignment again. I am not sure if you had a chance to contact the Canvas Help Desk or not, so I'm not sure if they had any suggestions for you. It would be best for you to contact them directly rather than me being the "go between" to contact support. Since you were the one who experienced troubles with this, they would be able to better help you than going through me. Hope that makes sense.
One thing I've seen suggested several times for students is when you have a lengthy written assignment to turn in, maybe compose all of it offline in a Word document or other word processor application on your computer. Then, depending on how your instructor wants it submitted, you can either attach that document to the assignment, or you can copy/paste the text from your document into the assignment. Here are a couple Guides on how you could do that:
Hope this will help!