This technique is by Marcy Tilton. 'This technique is straight from the workrooms of French couture houses, and works for small pieces of bias and longer/larger pieces.'
Bias binding stretches out to become longer and narrower which can give an uneven look to a bound edge. Cut the bias binding an inch wider than you need and then do the following.
Press to take the stretch out
Position the bias cut strip on an ironing board
Press, stretching gently
Re-cut to desired width
Take the pressed strip back to the cutting table
Using a clear ruler and rotary cutter, trim it to an even width
Keep the length longer than needed to make it easier to handle - you can trim after sewing