What I found really helps with the HSTs, is starching the fabric, and using a throat plate with a single hole.
I also use my dual feed (could use your walking foot) for piecing as is gives better accuracy.
Remember to change the throat plate back when zig zagging or decorative stitching. You go through less needles if you do. :)
The single hole throat plate is great for stippling/FMQ as well. I use it more than the other throat plate so it was well worth the purchase.