You should be fine. I always buy Butterball frozen. We prefer the Butterball frozen over the fresh because it is more moist. Costwise, they are about the same at my market.
I currently have an 18# Butterball in a large bowl with a towel around it in my fridge thawing. I started this on Sunday. It just slowly thaws in the fridge. IF it is not thawed as much as I feel it's needed, I will put it in some cold water in an ice chest by Wednesday. Your defrost time should be fine.
I stuff my turkey early on Thanksgiving morning and slow roast on about 300 for a couple of hours, then according to my thermometer (which is a great one and spot on with temps, has an alarm to alert me if temp gets to a temp I program it to go to so I won't overcook) I slow cook for several hours and then about an hour before we want o eat, I remove he foil tent, baste it well and blast it to get it nicely browned. THEN, it sits for about 15-20 minutes (continues to cook) before we slice it.
I never go by the cooking instructions, I follow my routine and rely on my thermometer. We prefer slow roasted on very low for several hours for moist and juicy turkey.
No don't throw it out. You can guess the weight and manage it. Take it to the grocery store and have them weigh it if it makes you feel better.
Now I have seen some cheapo no name brands at .79/# frozen but I am loyal to Butterball. I've not screwed one up yet!
Happy roasting!