Don't worry about the stings, they grow a new one every 3-4months & shed the old one. be careful handling the discarded sting as it can still be toxic.
the ray is severely underfed, feed BW, prawn/shrimp/ whitebait /mussel at least 3x a day, As much as it will eat, & it will eat more than you will believe.
I second this comment. Looks much too skinny and very oddly shaped. There is also a big chunk missing from it.
I think you need a bigger tank, and for now, no tank mates.
Another food to look out for is live earth worms. Try the local pet shop for them, if they sell reptiles they will probably sell earth worms. At work I normally feed the rays earthworms twice a day and they love them, if it isn't earthworms then I will feed them krill.