And small does not necessarily mean "weak". If it remains smaller than the others, it may simply have genes coding for a small plant. Not necessarily a bad thing.
I was hoping that might be a possibility. In bedding plants of mixed colors grown from seed, you are told not to just pot up the biggest seedlings, because some of the more desirable colors can come from the smaller.
DNA is a funny thing especially when there's hybrids involved. It should be interesting to see if there is a difference between the blooms for each size.
It just might be a mini for the rest of its life. As long as it is healthy it shouldn't matter.