Draw a two inch circle on paper, divide 360 degrees by 8 like you did,

draw a straight line touching the circle and extend it way out. Draw another line farther around the circle to meet the first line at 22 1/2 degrees, extend it well out.

Continue doing this till you have closed in the circle.

Now you can measure the length of the octagon lines where they meet.

There y' go

mo.