my quilt borders typically have odd shapes.
i don't cut the odd shapes until i'm done with the top this way nothing stretches out of shape.
i'll square up the quilt top - then i fold it in half lengthwise lining up the border for both sides and then i cut the shape, then i fold it in half widthwise lining up the border for both sides and then i cut the shape.
i do my border shaping free hand with the rotary cutter you don't need a ruler to cut a wavy line and by folding the quilt and lining up the border you'll achieve an exact copy on each side.