Toe up socks

I'm currently working on a pair of toe up socks for my mother. I've made two pairs of toe up socks in the past. I must say that I suck at the sewn bind off. On the other tow pairs I went up a few needle sizes so the regular bind off wouldn't be too tight. This time I'm doing the sewn and it is not working out well. I've done the bind off on other projects in the past and it went fine so I'm not sure where I'm making the mistake here.