You could rasp out another section of your horn (shown in yellow) leaving a raised band to catch the horn strap. "Engrailing" is just decorative notches cut in where the throat meets the body of the horn. Not necessary, but it looks cool!Nice looking horn.
Did you use the round file before squaring the end of the spout ? I worked on this one a while to get where I am and still have a long way to go. Also, where your strap connects on the forward end,is that engrailed ? I may end up doing it that way if I can't make a band from horn or wood. I do know that the band will have to be boiled if horn or soaked in water if I use wood to conform to the shape of the horn. I used square kitchen match sticks for the pegs in my priming horn. After a short soak in water, they go in the round hole.
I'm almost after the Southern Banded style but that may be too far advanced for a first time.
Thanks for the info and keep the ideas coming. I need them.