Linda,
There's a difference between the chance of getting a particular trait to show up and what happens when you're actually planting. On the average, you would see your dwarf trait one in four plants. But as you know when it comes to flipping a coin, you can flip a lot of times without getting "the average" outcome.
I took statistics and calculated the odds of getting a "1 in 4" trait.* While you would expect it to be seen in 4 plants, it would be within normal limits to not see the trait until the 16th plant. That means that it's not all that eyebrow-raising to not see it in 15 seedlings. You have grown 32 seedlings with no dwarf. Yes, that is eyebrow raising.
You could: 1) presume you've been unlucky and try another 16 seeds (easy to do), 2) presume something went wrong with the original cross and make the F1 cross again, or 3) bag all hope of the dwarf & concentrate on flavor in the F3. It could happen that you'd see the dwarf in F3, but don't count on it.
*(I bred lovebirds, and one set of non-blue parents gave me 15 non-blue babies. The 16th one was blue. Blue should be a 1-in-4 possibility. I calculated it out and seeing the trait in the 16th baby was really within normal limits.)
Nan