I want to sneak and look under girls' skirts and dresses.
Why do you want to engage in non-consensual behavior?
I don't know it feels so good
It might feel good to you, but it definitely wouldn't to the other person. It can be quite violating and traumatic to them, so I suggest you try to find a therapist to help you away from this.
I don't think it's wrong.
It's a harmful thing to do, and there will be consequences if you get caught because it's illegal and immoral. Think of the women in your family, would they want this to happen to them?