If you wash it and block it, it will straighten out the edges some. But when you “fix” it, then wash it, the fixing might mess it up again. I would fix it then wash and block the entire thing.
To ease your mind…when it is worn, or used, like a blanket, the edges are hardly noticed at all except by you…it is a lovely shawl as is and the border will just make it fit better and show that pattern at the back.