@5t3114 zigzag type patterns are inherently a bit wavy, but for this one you could make the edge knots flow to the outward direction. So the black knots should be backward, and white knots forward... for example like this pattern #148657 Don't pull the strings too tight and use equal knot tension on both sides to keep the bracelet from warping.
Another option would be to use the straight-edge technique by switching the left edges to backward-forward, and the right to forward-backward. Here's a similar pattern with straight edges built in #148655
unicorn547
