Circular spiral blanket that I eventually want to be rectangular (bad drawing included)

I was just asking to see if this was possible? I have a 3 color spiral that I started as 3 double crochet of each color into a magic ring and then gradually increased. I was wondering if there would be a way I could eventually make the spiral a rectangle? Or put a boarder around it without disconnecting the yarn? (It’s the stupid fuzzy yarn that sheds so it’s a literal nightmare) I have a terrible photo I drew as I’m not home rn