Nice looking horn. It is much easier to shape with the scales glued together, I use scotch double stick tape from the dollar store, a couple pieces will hold it together well. Taping or gluing also ensures your holes are straight, in line and that the scales match.
It is also easier to hold a thicker piece.
It appears you tang pin holes are a bit off center, could be the photo.
Now is the time to fix that, just take a bit off the one side, to center the hole. You want your tang end of the scale thinner and narrower anyway, especially if you are going to use a stepped collar.
Here is a good post on making horn scales.
How to make a traditional set of horn scales ... the way I do it.