Is it too late to make the bed far, far wider?

I’m in Texas/z8, too. I have a narrow spot in my back bed that gets about the same amount of sun as yours, and gets runoff.

Southern Wood Fern would look nice around your tree. This is mine (it’s much fuller now):

In the narrower part, salvias would do well. They appreciate the afternoon shade during our worst heat of summer. They’ll spill over the edging somewhat for sure, but are perfectly fine in narrow beds. IME, in our state, having grown too many to count at several homes — when in more shade, they tend to not sprawl as much, and stay a bit more compact.

This is mature purple salvia greggii (two) in a tight spot, last year:

You could also have daylilies, or phlox, or cannas, etc. There really are a lot of fine choices, keeping in mind most will spill over. You could also put a trellis on part of the fence and go up — plant a mandevilla on it for annual color.

So one example: ferns around tree and three salvia along the rest. Or, ferns with cannas filling in the rest. I would keep it fairly simple, as it’s such a small bed.

Thank you. I was thinking ferns at both ends. I’ll check into southern wood fern. Yours is beautiful!

I was hesitant for cannas as I worried they would eventually take over if I wasn’t diligent☺️.
The salvia is also a good idea.

Thank you for speaking from experience in our zone.

A wider bed was my initial plan but plans were changed and it’s mortared in.

Yes, they can be a pain sometimes! (Cannas.) :D These are dwarf cannas (yellow) and you see I need to move some soon. They get about 3 ft tall at maturity:

This is Phlox paniculata ‘Texas Pink’ on the left of the birdbath ... as wide as it’ll get, it’ll just get taller and flower. I can’t find last year’s pics. It would do well in your bed, I think, but wouldn’t flower as long as salvias.

Red greggii behind my herb sink: