If it's acting like "jello" you might have used too much glue. In the couple sinew backed bows I've done and from the advise on here--I size the bow with a thin coat of hide glue, dip the sinew into the glue, slide my figures down the sinew to ring it out, then apply it to the bow. It should be dry and hard to the touch in a day, maybe 2 with high humidity.
Or maybe you didn't reduce/cook the glue long enough. The test I use is to stick my index finger in the glue. Then tap it against my thumb. If my thumb and index finger sticks together in about 10 taps, 15 seconds, it's ready. Others might have a better technique.