Are you using a walking foot? If not, that may help with the puckers. I have found that the safety pins don't work that well for me. I lay the quilt on the floor (I have a large area in my great room that is tiled) and straight pin only the seam I am interested in stitching. After stitching, I press the seam, both top of quilt and back of quilt. Then lay back on floor and smooth, smooth, smooth. Then pin the next seam, etc...
It's a bit tedious, especially with a large quilt, but it works for me.
Good luck and I hope you find a method that works for you.