It's also going to curl into a tube in all stockinette. Do about 5 or 6 rows of garter stitch after the cast on and before binding off, then the same number of sts in knit on the beginning and end of the WS rows.
Is there a reason to make it that big? Most throws are about 40-45" wide by 60-70" long. Maybe the dimensions are in cm which makes it about 38x55".