No worries. It happens to the best of us. I actually tend to forget myself that there are two sizes. US-05 is my house, go-to yeast, and it comes in one of the big 11.5 gram packs. On the off chance that I use something different, it's US-04, which comes in 11.5 also. The last batch I did, I had to use a different yeast, as the place I have to buy from now does not carry Safeale. (they do now
) I did a 12 gallon batch with one 5 gram pack. Man was I scared!! It was SAturday, and they were not open again till Monday. I did what I had to, and pitched what I had. I got fortunate, and all went well. Had a very vigorous fermentation, and no funk in the beer. Just got fortunate, I guess.I'll not make that mistake again.