My mil and I made a queen size one this Christmas. But we made sure it was tacked, we like the look more.
ANY TIME that you are quilting a sandwich and it is thick I say that a walking foot is a must. Any place that sells sewing machines will have "quilting" accessories. Walking foot, darning foot, 1/4" foot etc. Also, some smaller shops that sell vacuums or do vacuum repair will also have them. You can also find them on Ebay rather inexpensive.
The first thing I would do is to refer to the owner's manual of your machine or their website to find out the shank size that you have. That or take your machine to the shop you are buying your walking foot at. It looks like a little box that attaches. It should also have an L-shaped metal thing that attaches to it. It sticks out the side and helps you guide your stitching, but I don't know if I would use that piece with such a large quilt. But a walking foot has moving feed-dog looking things on the top and it helps the ones that come on the machine feed all three pieces evenly.
The way Patrice said to do it is the best thing I can think of. She also had the suggestion of moving the quilt in your lap or adjusting how you sit every few minutes. You may be overworking your machine if it has to pull the quilt out of your lap too. A walking foot will make your world a whole lot easier!! And if a dummy like me can use it on her first quilt ever, then I'm sure you can!! It's almost like an extra pair of hands helping to get your sandwich in evenly.
I hope this has helped. Oh and when I bought my "accessory" kit from the sewing machine shop, it was cheaper to purchase all 4 feet in a set than it was to buy them individually. I spent about 50.00 or so, but 2 of the feet I use all the time. Whenever I want to experiment with free hand I use the third. The autobinding foot I never use, but that's okay, I have a hard enough time making it myself.
Wow..didn't realize I was going to leave a chapter in the book of responses. I saw the pic of what you had so far and it looked wonderful. Just take your time because it's so heavy. Make sure you take frequent breaks so you don't overwork your back or neck sitting in one position for long. Also, when frustrated you may want to go in the back yard and kick a can, but if screaming or swearing I would do that inside. You wouldn't want your neighbors to think that you were either being attacked or that you are a crazy person.... :mrgreen:
Hope this helps... ((((hugs to you))))
Melissa