I just started FMQ on my 6600 a little over a year ago and just started off doing samplers, then potholders and table runners. I attended a workshop with a quilter who has published several books and I have also purchased a couple of Craftsy FMQ classes that I can watch over and over. Both were confident builders.
I'm not perfect, but I do enjoy what I am able to accomplish now. I can easily FMQ crib, lap and twins but I rent a Long Arm at my LQS for anything larger than a twin.
Don't give up...you'll find your groove.