It’s totally normal. These aren’t clones, they are like any other offspring. Each will be a different genetic expression of the parents.
Humans are a great example - parents can have 3 kids and conceive them in the same conditions, birth them in the same conditions, etc etc .. and yet each will be distinctly different because they are different genetic expressions of their parents. Look up “phenotypes” of cannabis and you will get some good reading to understand this.
Don’t worry about it at all, continue what you’re doing and you will see the beautiful differences of your plants when growing from seed.