Virginia,
Sounds like you started your binding at a corner. I suggest you tear out about 5" of the first side and make your connection there along the side of your project. If you do this, you can make the "last corner" as you did the other three.
At the 5" spot, fold the raw edge on an angle and then tuck the other raw edge inside, trim excess and them sew shut.
Hope this answers your question.
Suzanne