You don't have to, but typically when people upload deviations to DA, they try to get rid of any blemishes or blank portions on their deviations, unless it is for decorative effect. Cropping the borders of this deviation would make it look more finalized and less messy/ unkempt. If you were going to turn this into your professor for a final grade, or if you were going to enter it in a competition or as part of a gallery then it is recommended that you crop the uneven white borders, which disrupt the flow of your painting and make it seem unfinished. Just a word of advice. You don't have to take it to heart, if you don't want to.
Don't worry, I've turned in dozens of assignments to professors and won plenty of competitions already, I know how to prepare my work This is just a scan of the painting. Deviantart is a casual place for me to put my work online so I can easily access it, so I'm not as inclined to go through the nitpicking to make the picture look perfect. It's close enough for me, haha