Is it possible to undo the top into quarters? These would be a more manageable size. Quilt each quarter to within about an inch off undone seams then join as quilt as you go. Hand stitching the back seam looks neater I think than trying to machine it down. Then go over the seam with a quilting line to match rest of quilting. Do this for each one and you feel the weight coming on and are glad you did it this way.
I do them this way as I hate having to manage a large quilt under a home machine.
If you don't divide you need to have something on your left to help to hold quilt up I use an ironing board. Gloves with grip, I use a new pair off ladies gardening gloves. And concentrate on the one area at a time just make sure rest not pulling.
Top tip plenty of patience.