Hm, this is an interesting thread. Let me first say that I've never worked with sinew myself. Although I've been reading about it, I've never done a sinew backed bow myself. So please take my advice with a grain of salt.
So let me get this straight. You are making a sinew backed osage recurve. At 68" in length. And the sinew is glued with TiteBond 2? I've got some reservations about that. An artificial glue such as titebond will not create the typical benefits that would get when you use hide glue. Your glue doesn't work with the sinew, but rather against it, so to speak. Hide glue consists of mainly the same proteins as sinew itself, and will form a matrix with the sinew. Titebond will basically form a matrix by itself, in which the sinew is embedded. This means that your bow ill not pull into reflex as the glue dries. Furthermore, it also seems that you used a LOT of glue. And glue is heavy. So you basically added a lot of weight to the back of the bow. This weight in principle slows down the bow, unless you gain performance by the sinew working hard. You can make this sinew work hard by making a short bow, so the sinew stretches a lot. But since your bow is rather long, this effect is negligible.
So I see two major draw backs for the performance of the bow. First, your bow is too long to benefit from a sinew backing in general. For a 28" draw (but you didn't specify your intended draw weight or - length), a sinew backed bow should be under 64" preferably. Second, you are limiting the efficiency of the sinew by not using the best glue. Titebond may work, but it is just far from optimal.
It's a really impressive 'first bow' that you are making; don't get me wrong. So far you're doing really well and the woodwork by itself would even impress me if this were your fifth bow. I just feel that this bow would be better off without sinew entirely. It probably shoots faster, better and more pleasantly without it. Although the sinew might be a huge experience for you and I'm sure you gained a lot of knowledge from applying the sinew. But I just think that the bow would be better off without sinew.