you want your finished product to look as good as possible. basically, you want to iron it in such a way that the side seams of the coasters are flat. you can use your chopstick to help you with this step too, if you find it helpful.
sew another seam with about a 1/4 seam allowance – although this is more of a “choose your own” based on how you want your finished product to look. this would be a good time to use any sort of fancy stitches you may want to add. add the seam all of the way around being careful to close the opening appropriately – making 