The sapling is too young to ID to species from the photos (flowers are a key feature used to separate similar-looking species). We found one ID key that separates Cornus florida from Cornus kousa (listed on that page as japonica; Benthamidia is the same as Cornus), but as you can see, it also relies on flower differences. However, it also notes a couple leaf structure differences that might be useful. Still, there are hybrid dogwood varieties with Cornus florida and C. kousa as parents, so the traits might be in-between the two in that case. If you acquired the plant at an Earth Day event, presumably (hopefully) it was the native species, Cornus/Benthamidia florida.

For the tree's long-term health, we recommend that any turfgrass or weeds be removed from around its base for at least a foot or more distance away from the trunk in all directions, and make sure any mulch used to cover the soil is not touching the base of the trunk (and is only laid about 2 to 3 inches thick in a flat layer and not a mound). As for mature size, that depends on the genetics of that individual plant plus its growing conditions, so we can only guess and say that both Cornus florida and kousa get around the same size (and grow relatively slowly): roughly 20 to 30 feet tall and a similar width. Often, these trees stay taller than wide for many years while young, then eventually widen and the canopy gets wider than the tree is tall over the long term. However, each individual tree can differ and will be influenced by how much sun it's getting and other factors, so it's only an approximation. Assuming it will eventually reach 20 feet tall and have a 20 foot branch spread about 20 or more years from now would be fair.

Miri