I still have to outline it.
I've decided that I'm going to use a fine pigment marker.
I could use a brush (or a mapping pen, which has a very very fine nib) but the chances of 'wobbles' are much higher. I don't know how many colours are in this illumination, but there are quite a few. If I have to re-touch the edges, going right through the palette again, I'll go nuts!

I've received some commentary, which is just great.

Kit pointed out that

• the 'cones' on top of the leftmost and rightmost flowers didn't line up (now fixed)

She very kindly printed out a copy of the work and took it to show her teacher, June Francis, a published calligrapher.

June said that I was doing everything correctly, but commented

• the margin was designed to go into a book. The margin extending over to the right past the text would therefore run into the gutter of the book. Since I am doing a single page, I should have shortened the length, especially of the bottom margin, to end more or less where the text ends on the right hand margin
  

Oh well. I'll know for next time. I remember having some thoughts about the length of the bottom margin but I wanted to include all of the 'cone flowers'.

• that the ascenders and descenders seemed a bit short.

I agree. I wrote it using 1 mm A/D to 4 mm x-height. I arrived at the 1 mm A/D height because I'd measured the x-height in 3 contempory documents, and this was the ratio used. (Note - of hand written scripts, not the text of the printed Gutenberg Bible). The normal ratio of x height to A/D in Gothic Textura Quadrata is 5 or 6 n.w. : 2 n.w. (Harris, Calligrapher's Bible, and Lovett's Guide to Calligraphy).
A lesson in using judgement as well as design information from historical exemplars!

The final scan of the bottom margin only will show it with outlining. Kit is very kindly sending me up a suitable pen.