That kind of laddering can come when you move the fabric too fast on curves. Many/most of us have done the same thing when starting I would guess. You need to speed up your machine some and then concentrate on moving the fabric at a consistent speed. It is very very easy to speed up when doing curves! I've heard recommendations about quilting to some type of music to keep your rhythm constant. I find I sew best when listening to an audiobook!

Pam