It's a florist or greenhouse hydrangea - that's why such a tiny little thing. I would not plant it out at this time of year - florist/greenhouse hydrangeas do need time to get acclimated to a garden setting before winter and I think you may be cutting it too close. Potting up and moving into garage for winter is a great idea. You can leave it in the garage all winter if you like (may be safest move) - just make sure soil never completely dries out......keep barely moist.

In spring you can gradually acclimate it to the outdoors and then plant in the ground as you wish. I'd not expect too much in the flowering department for a year or two. Florist hydrangeas are manipulated into bloom precociously and often do not rebloom until their own internal biology is re-established.

Here is a link that might be useful: Hydrangea macrophylla 'Ravel'

Leave it outside against your foundation until the leaves change color and fall off naturally, then garage all winter.

Not guaranteeing any blooms in Spring this early in the plant's life, but should bloom after at least two years outside in zone 7. Just plant in a moist semi-shady location this coming Spring!

Ravel is a mutation of Merritt's Supreme that blooms pink with white streaks or vice versa. The color combo is rare and will pay off if they can bloom in your zone. I believe Lowes was selling a lot of these this year under generic Merritt tags.

Thanks much folks for the info and the link. (nice site)
I was leaning toward leaving it potted but just didn't really know.