Whats wrong with my molly?

Usually scratching means parasites, probably ich. I would treat for that. Are there any white specks on the fish's body? If it does have ich you need to treat the whole tank. It's kind of like a dog with fleas... they jump off the dog to reproduce & then jump back on. The parasites live in the water. I assume that if you are posting in this site that the molly is already in BW? Raising the temp to 87-89 will help speed up the life of the parasite & get it off the fish faster. I hope you can save it, but by the way it's acting, I'm afraid it might be a goner.

I had a swordtail that did that, he and another sword used to fight all the time. his fin got torn pretty bad, and he could only turn left. sharply.

so he keep 'chasing his tail' to the left.

how to fix it? i dont know, but i thought i'd reply anyway.

Here are my 2 theories:

1) possibly he became so weak (for unknown reasons) that he got stuck against the filter causing the curling to his body

2) something internal has caused his spine to curve.

Does he look really thin? how is his breathing? How big/old is this fish?

I agree with Puffer punk that it is most likely too late to cure this mollie, but whatever info you can get from him, may be helpful in determining if you other fish are at risk?