Then pull out the elastic far enough to fold it on top of one another and straight stitch back and forth to join the two ends of the elastic together.
Then feed them back into the "ditch" you made for it and join the open edges of the sock and straight stitch across that 1/2 inch gap to close it up.
That's all - you are finished. You can vary this by just zig-zaging the bottom edge too to give a lettuce edge finish.
Have fun with these.