Gannyrosie -- that is beautiful! I actually think it looks great with a big black and little white backgrounds as it looks right now. I think the suggestion of sewing it to some kind of interfacing and then turning it inside out to get the edge smoothed before you sew it down is likely the easiest way. If you don't like the stiffness of interfacing on the wall hanging, sew right sides together with muslin (is there a back side on muslin?) and then turn inside out before you sew it down. Hand applique will be a lot easier if you sew it down to some kind of a lining first. This is going to be a blue ribbon winner!
Just beautiful!!
Hiya Barb! Welcome to the 2023 gang!