do you close the pins when you put them in or after you get a few in the fabric.
If you are closing the pins when you insert them that could be causing some of your problems. It is better to pin a section but not close and then go back and close.
also as you quilt, be aware of the back by putting hand underneith the quit and smooth it our and make sure all layers are smooth. Little difficult with a large quilt but you can do it.