Oh gosh, I just found this thread too, sorry I didn't reply sooner. I think I know what you are talking about because I have had these problems too. For me, the fabric does overlap a lot. Just practicing over and over seems to help (I know, that is not exactly the best advice, but...).
When you place the podaegi on your back, try securing the straps/fabric under your armpits. This is my little trick. So, while I amcross the fabric beneath the baby's legs, I try to keep my armpit area really tight, and get the fabric as tight around my chest and as high on my chest as possible. As far as getting the fabric straight, I usually fix that after she is tied on - Just pull it through and tug it straight.
Does this help at all?
Let me see if I can get some pictures up...I'm terrible at getting stuff like this done though.