Congratulations on growing your clematis from seed. I put in new plants last spring and again this year, and I found that the first year blooms were smaller than this years blooms. It also depends on the time of year that your clematis is blooming. Here is a comparison of Niobe in the spring, and a bloom from today which is 1/3rd the size of the spring blooms. For my clematis that tend to rebloom, the later blooms are smaller, and some that are double in the spring, tend to bloom as single later in the year, so the temperature must also play a factor. I'm no expert, but I wanted to share what has occurred in my garden. Good luck with your new baby.