I always hand baste the centers before sewing down because they get so bulky. Since you are joining some parts on the bias edges, you can have some stretching - I think that is the buckling babeegirl was talking about.
Also, do not let your eyes fool you when working with the diamonds - in order for them to join properly in front, they will look offset at the edge. Maybe I am the only one who has had the feeling it did'nt seem right, then resorted to pinning and basting until I learned better.
Good job!