I make my rag quilts with 3 layers of flannel, or sometimes 2 flannel and one corduroy, and I don't sew an X because it's unnecessary to hold the layers together when all 3 are sewn at the seams. I don't have a problem sewing the rows together. I think you're having more trouble because the dimple plush fabric is slippery and thicker than the flannel. I would try pinning the fabrics together pretty closely so they don't have a chance to shift while you're sewing. The advantage of this over glue would be that it will hold all 3 layers together. You would have to insert glue in between 1st and 2nd layer, and also in between 2nd and 3rd layer to do this. I think pinning would be faster and would leave no residue.