waterbuffalo horn build along would have been a better title since I see no sheep!
It was very clear from the beginning pictures that you did not have nearly enough surface scratches on the back of the bow for the sinew to adhere to, if you would have also wrapped the sinew while wet with some nylon cordage you could have prevented lifting of the sinews.
Without building up the sinew layers at the handle you will have a big rubber-band instead of a bow, the even distribution of the sinew over the length of you horn core which looks to be an even thickness throughout will not allow for the stiffness in the middle that you need. I might suggest adding a piece of horn to the belly with hide glue then wrapped with sinew after you have all your layers added, this might add the stiffness needed in the middle. You could also take some of the reflex out by clamping the middle of the bow to a board and pulling the tips down with some anchor ropes before the sinew cures to much. To much reflex tends to make the bow want to twist in your hand when stringing and makes the overall bow unstable.
Just some food for thought.
Good luck with your project.
