we need pics of your stuff to help
and to succeed you'll need a bigger tank hands down
otherwise not to sound rude but return the ray to the fish store
Pics would help.
My guess - pelvic bones on a skinny ray.
I think most people initially feed blackworms to their small rays in the US to get them feeding and get some weight on them.
Loads of discussion about it in other threads if you have a look.