"It's not worth it" is correct.

Hello,we say something is not worlth .

Alice where are you chatting from??

It's not worth it and it is not worthy of you. It is a worthy cause. He does not know his own worth. I am unworthy of this honor. That car is not worth more than $300. It is not worth my time. Someone who is more worthy should receive the scholarship. It is a worthy cause. I paid much more than it is worth.

To understand "It's not worth it." an example will help. Don't cheat on the exam. It's not worth it. Presumably there is some value one might get from cheating on an exam. Namely, possibly a better grade. But there is also a cost. Not to mention the moral cost of doing something wrong, you might also get caught and expelled from school, so the first "it" refers to the benefit of doing something. The second "it" refers to the cost. The benefit is not worth the cost. To understand "worthy" another example will help. "He is not worthy of her love." In this example, someone claims that He does not _deserve_ her love. Being "worthy" or not "worthy" of something is a kind of moral statement about the person who is worthy or not worthy. Worthy = good. Not worthy = bad.