Now that you have your buttonhole sewn you have to cut out the middle.
Turn your fabric to the wrong side and pull the needle thread through to the back. (Do this by giving the bobbin thread tail a little pull, the needle thread should poke through. Use a pin to pull it all the way through to the back.) Tie the bobbin and needle threads together and clip the ends.
Turn the fabric back to the right side. Pin the top of the buttonhole as pictured above, right below the top tacking stitches.
Insert the tip of a sharp seam ripper into the bottom of the button hole. Make sure you don't pierce the bottom tacking stitches. Push the seam ripper through, opening up the buttonhole, until it hits the top pin.
And here is the finished buttonhole!