I would assume the darning plate you put over the feed dogs is for straight stitch, small hole?? If so, don't use it for FMQ. I took a class and the instructor said not to lower feed dogs. It went fine. I usually do lower them though but it might not be something you must do.
try doing FMQ with the feed dogs up as usual and don't use that cover plate. use your main one that hopefully has a wider opening. good luck. sometimes it's just a bad day over all.