Welcome to the QB from SE Michigan! Log cabin blocks have been made in different sizes for what now is centuries. You may want to make your logs cut at 2" so they come out at 1 12" logs is all Or you could still make them cut to use your original plan but your center will just be smaller. Nothing is set in stone. Just trim to the sides evenly and keep adding the logs as you go. Jump right in and join the fun here. I would love to hear more about you. Again Welcome to the QB.