I totally agree with Salmonac. And I agree with your plan too. I'd pick up about 6" worth along one side...3 for 4...and knit it along until the appropriate number of rows...and see if it ripples, or puckers, or looks just right. I'd do this as an exercise. As a "swatch" attached to the blanket. It can save you much frustration if you need to modify what you did.
I've knit many a "swatch" that is out-of-the-box...as a trial run before really committing myself to the real deal. It's part and parcel of the work. And totally worth it in the long run. The edge of a blanket is so very important, and I hate to see blankets where a trainwreck-of-a-border is just left like that. Ugh.
Really, same principle applies to button bands. Ugh. They gotta be spot on, IMHO.