This trick is bag related! When you’re stitching the sides of your bag, you want to sew in one direction, i.e. stitch from the top to the bottom on the left and then the top to the bottom on the right.
Once you’ve stitched both sides, you can stitch across the bottom. This will prevent your bag from pulling in one direction. If you stitch down one side, across the bottom, and back up the other side, your bag will likely lean a little to one side.