After I kill the wanted guys it keeps going. Somewhere I saw you are supposed to go back to your horse and nudge it. I walk into it I try to jump on it the game just stays. How do you end it after killing the gangleaders?

I don't remember how to end it, but I do remember being surprised that 1) it didn't end when I expected it to, and 2) it finally did end when I didn't expect it to. I remember it being kind of stupid, though. I suggest going to YouTube and watching a playthrough of the mission to find out how to end it.

I realize this is an old post, but in case anyone else is confused by this: you have to "use" your horse, the same way you would open a door. The game refers to this action as "nudge" and I think the default binding for it is the spacebar, although I changed it to E since that's the typical binding in more modern games.