Holice

If your bindings don't work - irregular, mitres not even and accurate I would wager (if I did) that the problems are:
innacurate and inconsistent seam allowance from the beginning of the seam to the end.
It is easy for the seam allowance to veer out or in at the beginning and end. I believe (as I did) to lose control especially at the end. This can effect the way the mitre will fold.
If your mitres are wonky - rabbit ears, then fold the binding back to see if the seams remained true. If not, then rip out and restitch.
Whatever your seam size might be - as you come to the end of the seam toward the corner, then stop a couple stitches before you get to that point - be it 1/4" or 3/8" or whatever. Back stitch a couple stitches and take it out of the machine. Then start the next seam with needle just catches the edge of the fold. this will hole the layers until you can aralign the binding with the edge.
Also, when you fold the binding to make the mitre, then be sure the fold and all layers are 90 degrees.

Guess this is more than #1 but it works.