I have a quilting magazine with an article about Angela Walter's and she also shows how to do some FMQ designs etc. There are close up pictures of some of her quilts and guess what...the stitch length is not consistent. So, if a "famous" FMQer can have uneven stitches so can you!!! Besides, when your not sitting 8 inches away from the quilt (as you are while quilting it) you won't notice the stitches are uneven.
Try no to be so hard on yourself, I'm sure it looks fine. We are always our own worst critique right?