A 1 1/2" log IS really narrow. They do come out smaller than bakery biscotti - a lot smaller. I cut each log into 20 pieces, and thus ended up with the 80 called for.
If it makes you feel any better, mine aren't at all uniform either. I found the batter pretty sticky and hard to get in a nice even log. However, when you cut them on the diagonal, it evens them out a *little* bit.