I love machine applique but learned that it is not necessarily a fast process. Sometimes I have to stop and pivot every 1, 2, or 3 stitches. Unless it's something I'm making for my mother...who has worse eyesight than I do. Then it's pedal to the metal!!!
I did learn (the hard way) that the right swing of the needle should hit just the outside edge of the applique. I always tried to make the zig zag stitch straddle the applique. By using the edge of the applique as a guide my stitches became much more even.
Be gentle with yourself. Progress not perfection!!!! You're stitches look great and will only improve with time.