I'm so glad that I asked, you all gave me the push to make the right decision. No turning back now, I've just sandwiched it all together and it is laid out on the dining room table ready to be quilted... With no border
Also, I measured again and had enough length of the lighter brown to make the whole of the backing fabric, so I'm very happy with that too. I'm going to sandwich a few scrap pieces together and have another try at FM in the morning. How to get it neat is escaping me at the moment, but hopefully, this might turn out to be my first quilt I attempt it on.