Bias tape help desperately needed

Hi there lovely people, I was hoping to pick your brains on the subject of bias tape, as I'm a little bit stuck. I've used it to finish edges before and I've also used it decoratively along both curved and straight edges. However, my latest project requires the use of bias tape along a sweetheart neckline and I just can't seem to do it! When I experiment with pinning the bias tape, I lose the detail of the neckline and end up with a round one instead of a sweetheart one. I've posted a picture of the pattern and my cutout fabric so you can see what I mean. Any useful hints, tips, advise would all be gratefully received.

On a slightly more positive note, drop by my blog if you're interested in seeing more pictures of my best finished apron yet: