@Ali_K115 for the center part with 4 knots of the same color, make sure those knots are close together and tight. There's naturally a space in the center so it can get wonky if too loose.
Also, if you look at the structure of the pattern, notice the path of underlying strings that come to edge at the triangles (at rows 10, 16 and 28 etc). Be sure not to pull those too tight as you're knotting around them because they can "slip" through previous knots which shortens their path and pinches the bracelet inward, and also pulls that center diamond I mentioned earlier outward, making it look flatter. Every few rows just adjust the knots a bit to make sure they're nested in the proper position. For those triangle edges, sometimes I take a pin and wedge it in between to keep the "corner part" out to the edge instead of shrinking inward, if that makes sense ๐
Most diamonds and zigzag patterns have a tendency to get wavy, but you'll get more uniform diamonds with practice and consistent knot tension ๐
yamomma
