confused about the throw...

Ok, so the Yarn Girls tell me (in their book, of course) that by knitting with US 11 needles, I'll only need to knit 40 rows to have 40 inches of blanket...but uh, what they don't mention is that you need bulky yarn for the whole thing to get this thickness. Sadly, I'm not too clever and didn't realize this BEFORE I opened up all my (thin) yarn and knit about 15 rows...so now I have at least 25 rows (it's hard to count cause they're so irregular) and only have 3 inches. WAH!
I bought some Lion Brand Chenille to bulk it up and am using that every other row...but I'm worried that I'll run out and I really don't want to buy any more yarn for this stupid thing...grrr...