Congrats on the finished product! While it wasn't easy, I recently finished a king sized quilt on a machine with a throat size of about 6". The issues you see on the back may be from a tension issue. The best way to fix is to make a practice sandwich from scraps and play with the tension until you get what you want. I usually dropped the feed dogs, set the stitch length to zero and then set the stitch speed at fast.....then it was pedal to the metal and let her roar! Really tho, consistent speed while moving the fabric is key to eliminating stitch problems, especially eyelashing on the back. Good luck on future quilts!