I made a mat out of a cushion-y shelf liner product to place under my machine. I need to prevent my machine from "walking" across the table so it will fit in the free arm slot when I fold the extension up. You could use other things like old mouse pads, yoga mat, etc. You might also have some vibration coming from the original cut-out space, so wedging pieces of the matting or some foam could keep that from moving while you sew.