I really like how your quilt turned out, and your SID looks great. Go for the wavey lines - it's YOUR quilt!
The SID foot is the one with a straight thin metal piece hanging down perpendicular to the foot right in front of where the needle will sew - you can see it, and use it to guide the foot along the seam.
It's also called the edge-stitching foot. If your machine allows you to move the needle, you can move the needle to the right or left and stitch the edges of - whatever you want to stitch the edges of! Quilt, cuffs, collar.