Sorry, I only saw your first two pictures when I posted. Your third pictures looks really good. When I practice I use 2 distinctly different colors so I can see what is actually happening.
I am just guessing, is your top stitch a bit tight? You can adjust this by loosening your top tension. Be sure to use good thread on top and bottom..not surger thread on a cone...makes a big different on my machines.
Your third and 4th pictures look very good. You are doing very good controlling your movement which makes for smooth stitches. Like I said keep practicing and experiementing.