Planning, planning, planning.

First make more binding than you will need as your insurance.

Then lay it out to check it out.

However, as you get toward the end of each side recheck that the seam won't be at the corner. If it is too near then cut the binding so it is shorter than needed and resew it together. Thus you won't have a seam at the corner. Now you will understand why it is better to make your binding more than you will need.