Everything gets better with practice and you’ll start to pick up on those areas where you think you might get bunching of the background fabric. My guess it happened on a large size piece. There are many times where I’ll use 3 or 4 of the Clover Applique Pins, working a couple of inches ahead of where I’m appliqueing and pulling out my basting threads. Have the pins run parallel to the seam line just far enough down so your seam allowance doesn’t hit them when you turn it under. That’s just enough to keep things from shifting on larger pieces and you avoid the bunching. I hope that was clear enough to understand. Yours is a good question and maybe I should add a few more diagrams to the tutorial. I appreciate the feedback.