Before you do anything more to your hair . . .
. . . rest and see if you can figure what you did "wrong." With planning, you can join diamonds so those center seams are paired--one on grain, one bias. That helps.
When you set in the squares/triangles between the diamonds, don't stitch past the dot. When you're in the middle of a seam, stop a stitch or two before before the dot and back stitch. When the seam is made, pull out any stitches that are in any of the seam allowances. At the outside edge of the block, the seams can be sewn from the raw edge (ignore "dot" rule).
When you join the quarter units together, the center has to match then--you can't adjust when all 8 are together.
If you decide to unstitch, do it by clipping the stitches from one side and pull the thread out from the other when it's loose. You don't want to pull on the edge of the patch and stretch it more out of shape.
Press all the seams in the same direction, working around the center. They should marry to make matching easier.
Use fine (.05) pins and fine (aurifil or similar) thread when lots of seam allowances meet. It helps keep the points crisp.