A good night sleep will work wonders. You can tackle it fresh in the morning and it sounds like tension problem that you may have to fiddle with. The Superior Thread co has a nice diagram for how to get a balance stitch and I use it so often that I printed it out for myself. It has the little stick figures that tell which tension you need to adjust. It could also be what you are trying to quilt through. Before doing any FMQ I always try a sample on a scrap sandwich of the same fabric and just sew a straight line to check the stitches. As someone mentioned, you have to put the foot down even though it doesn't rest on the fabric to engage the tension on the upper thread.