Del has given some solid advice. Listen to him.
One major problem with your stave, is that you messed up the thickness taper. A bow (and especially a longbow) needs to have a fluent thickness taper. The handle is the thickest point (and the widest too in a longbow) and the thickness should reduce
gradually towards the tips. The final few inches of the tips can be a little bit thicker again, so you can make them narrower, but in a longbow they are generally the thinnest point. Everything in between needs to follow the thickness taper from thick handle to thinner tips. If the back has a bulge, due to a knot that was nearby, the belly should follow this bulge. You didn't do that. You shaved the belly flat. That created a thick point at the knot, and a thin spot directly after the knot, where the sapwood dips down. Tape a caliper and measure the thickness taper carefully. In order to get a good thickness taper, it is possible to remove sapwood as well. You don't have to stick to the belly side, as Del explained. Just make sure you don't step through several rings at once, causing a steep angle ring violation.
That purple discoloration worries me a little bit. It happens quite a lot in yew, especially near dead wood, such as knot inclusions. Usually it's a not a problem, but that grey discoloration of the sapwood near that purple spot is a bit worrisome. Also because that is right in the middle, where the bow is currently bending too much.
You are welcome in my workshop near Hilversum this weekend. That's probably a bit closer to you than Del, who lives in the UK
Although I don't know nearly as much about yew as Del does, I've made quite a few yew bows and should be able to help you out. Hilversum shouldn't be too far away from you. You would be welcome either next Saturday or Sunday. Please let me know.