I can't seem to get the harness on our new True Fit tight enough. Or at least it doesn't seem to stay tight. And I HAVE made sure that all of the slack is out of the bottom first (around her hips). I just don't get it. It doesn't even seem to lay flat against her stomach and chest....but only at her shoulders. Am I doing something wrong?? Every time I tighten it up, all I have to do is pull a little bit at the top near the chest clips and it gets looser.