Reduce the top tension, the monofilament is pulling the blue cotton thread to the top...
Please, do keep at the FMQ. The only way to get better and more comfortable with it is to practice on something real. It really is so much fun...
I'd recommend testing your tension adjustment on a scrap sandwich made from the leftovers from your quilt. It doesn't have to be big...just big enough to do some test stitching.
Julie