I've had the same problem. I've tried using many stitches. YouTube has a lot of tutorials for different ones. The ladder stitch was really invisible, but i had trouble keeping it tight. I finally settled on one where you lay the 2 pieces flat and put wide tape behind them and then stitch. It worked best for me, but everyone has their own favorite. I used regular sewing thread at first but it was a bit hard to hide. Finer Aurafil worked better for me.