I cut my bias a lot wider than required for the finished stem. I use those white plastic strips that are used to bundle items together and have a slot at the end to tighten. Clip off that sloted end, the other end is slightly pointed. (Sorry, I don't know the techincal name but know they are lot cheaper than the bias bars. They also cool quicker than the metal.)
Fold the fabric in half lengthwise, use your cording or zipper foot and stitch along the edge of the white strip - really crowd the strip and slip the strip along the entire length of bias as you stitch. Before removing the strip, trim very closely to the sewn line. Owing to the crowding of the strip, wiggle the seam to the underside with the plastic strip still inside, sliding it along until the entire strip is pressed; and finally remove. You may also use a spritz of sizing to dampen before pressing, I do as it give a crisp edge. -- This even works with long, long strips for stems that may have to be seamed together.
PS: I prefer sizing, as spray starch leaves a white residue.
Suzanne