I think it's a bluntnose ray.
Bluntnose Stingray
Dasyatis sayi
Size: to 3 ft across
Habitat: Soft sandy bottoms, depths from shallows to 1400 ft.
Notes:
Potentially dangerous
The commonest inshore ray. Long smooth whip-like tail with stinger but no fins. Roughtail Stingray similar but larger. Smaller Atlantic Stingray and larger Southern Stingray may occasionally stray this far north as well.
Stinger: These covered with poisonous mucous and backward-pointing barbs, like a fish hook. The greatest danger, however, is from infection. Injuries are common among surf fishermen in southern waters who accidentally step on the animals. An embedded stinger will not pull out, and generally must be removed by surgery. Otherwise, it will slowly work itself inward. Stingray wounds can take months to recover from.