I am certainly no expert but it appears when you tried the 2 stars you bottom thread was not cooperating. Did this do it more than once? I have found on certain fabrics, that when you change direction you may be going either across the grain or with the grain that they balk doing this. I see your top fabric is denim. Try using two fabrics similar to you bottom fabric and see if it does the same thing. Try moving at different speeds. Sometimes heavier fabrics require a slower movement. Hope these are some suggestions that might help you resolve your problem.
Your stitches are nice and even and your swirly movements look nice and smooth. Keep practicig.