I don't have that exact machine, but I do have a Brother. When you siad you had tried several different quilting stitches, I'm not sure what you mean. Don't set it on any fancy stitch. Most people do feed dogs down, but a few prefer up. Stitch length is generally set at 0.
You will get tons of ideas here on the board, but another good place is YouTube. Just type in Free Motion Quilting. There are 100's of videos. Leah Day has many helpful one.