sunflowers are pretty aggressive...i get away without any chemicals by timing the discing/seeding/weather. Put them on a bit heavy (broadcast) and once they canopy out, the weeds are toast.
With what you did, you'll be fine.
Also, as for timing of growth and hunting dove...I do not condone this, but when I worked for the missouri dept. conservation, once the late start sunflowers were headed, we hit them with roundup a few weeks before the dove opener to dry them out, and then mowed some strips. It worked, but I'm not a huge fan of chemicals. Only reason I offer it is as a potential option if you're concerned about timing.
I don't plant my sunflowers for dove hunting, and mine aren't even in the ground yet this year...but I fully expect them to do completely fine. Plenty of grow season left for my needs
