I am wearing a size 38 Birk, which is normally the size someone would take if they wore around an 8. In a normal women's shoe, I wear a 9 or 9.5. I even have some 10s. So right off the bat I think you are wearing too big a Birk. From your description, it may be too long. If it is, the arch will hit you in the wrong place. And it will hurt.
Your heel should really rest back in the heel cup. I mean, it should be right up to the rear of the heel cup before it starts to rise up slightly. The heel cut is NOT the place where you want an extra 1/2" of room. Your toes should be about 1/8 inch in front of the ridge that rises up all around the toe. These are not shoes where you're supposed to have "give" in the length. You may have some in the width, but the length is more important because that determines how the arch support supports your foot. Don't give up -- these are good shoes. I'm not like Pinkee or others who have been nearly 100% relieved -- but I sure like them and I did just order my 3rd pair. Keep trying if you can.