I am using a Moby wrap with my 6 week old and love it! However, I don't think I am tying it quite right - when I put her in everything seems fine - she is nice and high up on my chest and very secure, but after about 20 mins of so I notice that she is starting to very gradually slip down. It happens very slowly, but this morning I had her in it for about 2 1/2 hrs and by the end her head was 3-4 inches lower than it had been at the start. I am following the instructions that came with the wrap, but I am sure I must be getting something wrong, as I am sure this isn't supposed to happen.
I know it is difficult to tell without seeing me tie it, but any ideas what the problem might be?