For future reference, one thing about putting curve in a patchbox hinge is that it should be done before the knuckles are cut and the hinge assembled. Otherwise, you are going to open up gaps in the top of the hinge. You are just going to have to do the best you can with what you have. When forming a patchbox, I don't put as much curve in the hinge itself as the metal fore and aft and to either side of the main body of the hinge. This works out well as it is harder to bend the hinge section. I have a hard maple form that I use to form brass boxes. For iron/steel boxes, I use a fuller and swage block at the forge. All of this is before the knuckles are cut. You do have to get the curve the same (or pretty close) in both the lid and the finial.