Thanks for all your replies. I went to Joann's today and got the 12" one for 50% off - $11-something. But I really wanted the 18" one so came home and went to Joann.com. The 18" one is not included in the 50% off quilting notions that expires tomorrow.
Oh well...I'll use the 12" one happily.
However...I think I will put some markers on the edges where I need to cut just in case my brain fries adding 3 1/2" together as I move down the fabric. :)
Thanks again - I'm looking forward to using it.