you are taking a lot of steps- and making the whole process awfully difficult- just set the seam- flat- one side- then open the fabric with the seam up- use a chopstick or something like that (I have a bamboo crochet hook I use often) to start opening the seam- if you feel you need steam go ahead & steam as you run the tip of the iron down the center of the seam- wooden chopsticks (given away free at Chinese restaurants) are very handy 'gadgets' in a sewing room- they will open up seams nicely without burning your fingers.
