Hi, I know this advice comes too late for this build but in the future if you find yourself lacking the right size drill bit, but you have a spade bit (the flat headed ones for wood) that is larger than you need, they can be modified by grinding/filing down the sides until you get the desired size. From my experience this is easier to do on the cheaper ones as they tend to be made of softer steel. Just do your best to try and keep each side equal from the center as they can be quite awkward to use neatly if you end up lopsided.