OK. The other possibility here is that this is a "Florists Hydrangea" a type of mop head that is green house grown specifically with big blooms showing as a gift plant and sold in grocery store floral deparments or florist's shops. Few of them do well when planted outdoors. But, because of the warm zone in which you are located, it's possible it might grow fine for you. Treat it like a mop head. Give it a place with morning sun and afternooon shade. Do not prune, unless absolutely necessary and then only immediately after flowering. Mop heads flower on old wood. If the old wood is pruned off or killed off by a winter freeze the flower buds for next year are gone. If you can, also pick a sight that will allow for the ample moisture that hydrangeas need but that is also well drained. Keep it well mulched and don't allow grass to grow around the plant roots. Not knowing exactly what kind of hydrangea you have makes it a little risky but that's the best cultural advice for all mop heads. I hope you can still have some fun with this plant even though it might sound like a lot of trouble. Getting it off to a good start is the most important thing. If you do find out it's another type of hydrangea alltogether let me know.