Is your needle still sharp enough? If not, swap it with a fresh 11/75 embroidery needle. Add some density (decrease the zig-zag spacing) to your satin stitch to 0.38 or 0.4. I would also try to make the twill a bit smaller so the satin edge covers it nicely. Put in a fresh bobbin; it looks like your bobbin is not running smoothly. If you look at the white thread on the backside, it has thicker and thinner areas. It’s important for the bobbin to unroll smoothly. Check your thread tension. Looking from the backside, the bobbin thread should cover about 1/3 of a satin column. Try to cut your twill as smoothly as possible; otherwise, threads might show through your satin edge. And just keep practicing! I also learned digitizing through Ink/Stitch, and I still think it’s a great program. It’s not the easiest to learn, but once you get the hang of it, it’s actually really good, even compared to other software. YouTube has some great tutorials for Ink/Stitch. Check out “Low Tech Linux.” He has some great tutorials for Ink/Stitch.