Finally decided to find the plaster, emulsion paint and PVA and coated my stitched sample with the mixture. I decided to coat the back as well as the front and, whilst playing with the piece, discovered it made a nice tube (ignore the pin holding it together!). It is only about 11 cm high (just over 4" if you struggle with metric measurements like me).
It is now laid flat drying out before I paint it.
Realised that it probably would have been easier to stitch if I had plastered the calico strips first. I think I may have avoided having to hem the edges and it would have made a much firmer fabric to work into.