LRC,
I agree with Sue, either you would need to use two strands of sport weight to equal the worsted weight, or you would need to increase your hook size with a single strand of sport to maintain the same guage (both stitches per inch and also rows per inch)! That would make the sport weight rows look more lacy, but I don't think it would match the look of the rest of the blanket.
If you like the sport weight, you could use it for socks and buy worsted new weight for the blanket. (Yes, just an excuse to increase your yarn stash.)
--Jack
