Well, it's a little hard for me to tell from the photo, because you're looking at the bottom of the knitting, but here's my guesses:
- Keep in mind, stockingette stitch curls, so you may just be seeing that.
Don't knit too tightly, if you can help it. If you cast on tightly, it may be hard for you to get the needle in.
Be sure to watch the videos several times to get the flow of things.