This looks like it could be a lacecap hydrangea - it is normal for them to have florets around the outside

What you have is a lacecap type hydrangea. These produce flattened flowerheads that have an exterior layer of sterile florets - those with the larger, showy petals - surrounding an inner circle of fertile florets. These are the tiny, what appear to be unopened buds in the center. This is entirely normal for this type of hydrangea flower. Yours just have not yet fully opened.

btw, your duplicate post will not show any responses because you linked to a FAQ forum. You can't post to those.

Yes. It's fine. That form is just its nature.

Big Leaf Hydrangeas can produce either mophead form blooms or lacecap form blooms. This plant produces lacecap form blooms. Not sure if you were aware of that when purchading it; the pot may also have been mislabeled thus causing your confusion. My own Nikko Blue hydrangea purchase was a simikar surprisr. The shrub was supposed to be a mophesd hydrangea but when it finally bloomed, the shrub turned out to be a reblooming lacecap.