I scuffed up and primed the inside contact areas of the three pieces of the flap skins and then started reassembling them together with clecos. However, I quickly noticed that one of the flap hinge brackets wasn't in the correct place because it wouldn't fit through the hole in the nose skin. Realizing my mistake during yesterday's riveting, I drilled out and reinstalled one bracket and one rib in their correct locations. I remembered to bend the edges of the nose skin using the Cleaveland edge rolling tool, and then reassembled everything.
Then I got my first experience doing flush riveting on the nose skin. After a little bit of practice on some scrap material, I felt ready to tackle the first row of flush rivets. That seemed to be going pretty well almost up to the end of that row, when my rivet set slipped and left a little dent in the nose skin. I'll have to get some second opinions about it, but I'm leaning towards just using some body filler later. Or I could pull that skin off and hammer it flat from the inside. Alternatively, I could order a replacement nose skin ($38 plus shipping).
UPDATE: Vans Builder Support has replied and indicated that the dent is still airworthy and could be safely filled prior to painting. The risk of damage caused by attempting to remove that many rivets perfectly is higher than the reward.