Doris, I pin my quilts on my dining room table also. I tape the backing to the table with painter's tape. I don't pull it too tight though, just smooth and snug. I think, in the past, I stretched the back and then when it was released it just shrunk up and wrinkled and made a mess. That was my experience, anyway.
Also, I have found that if I start taking the pins out as I move from the center out that I can smooth out the wrinkles a little better.
The best advice I ever received on machine quilting was to worry only about what was under the needle. Keep it smooth and the rest will follow. For some reason that just made me relax and focus on just what I needed to focus on. Don't worry about the rest of the quilt, it will follow.
Bottom line, keep practicing until you find what works for you. :wink: