So, your going to do an inlay of a different species of wood to go in that channel. Here's a suggestion. First do what Gary said, then take a piece of plywood, use a jigsaw or band saw and cut a pattern of the curve you want to make.. Get the edge of the pattern as smooth as possible. Clamp it to your bench on top of your cutting board, and be sure the board is clamped with it. Determine the center point of your bit to the outside edge of the router base, and move your pattern exactly that far away form the line you wish to route., and make sure when you start, that you are going in the right direction. You want to be going into the cut. Not the other way, that's called a "climb" cut and can cause you some of the problems your having. You want the edge of your router base to run along that pattern without changing positions, Take a lighter cut. And, make two or three passes til you reach the depth you need. One more point, make your pattern longer than your cutting board.