As I was not happy with the result, I unpicked the weft today. Added extra black warp thread and started weaving again. I first wove basket weave on the edge but that did not work out well so changed it to plain weave. I should probably have added more threads for the basket weave to work well. I only added 6 threads each side. At this stage I'm not going to change it again.
This is how it now looks tonight. The bottom shot is from the back.