When I did my first one I had to use scrap fabric and mess with the tension a bunch before it looked right. Also be sure you lower your feed dogs. My machine has a free motion quilting foot that won't work properly if your feed dogs are up.

Good luck! It's frustrating I know, but I've done a few now and while I still have random issues pop up I have worked out most of the problems. Also a good tip is to remember to write down your tension settings, stitch length settings ect. so when you come back to do another one you already have a good set point.