From your pics, it looks like you are sewing too fast and haven't set your thread tension. The bobbin stitches are coming to the surface. You want the surface thread to draw down into the fabric.
I think you are trying to go too fast. I did at first and my stitches looked like yours. You'll have much more control.
Also, if your using a poly thread, be sure to wind the bobbins SLOWLY or the thread stretches and as you sew, it will pull up the bobbin thread.
I've been there and done all that. Hope this helps.