Had loop done CIN 3, biopsy came back CIN 3 nothing else found, 6 months on colcospy looked fine smear back cin3 again why? I'm confused.

Not all removed. The leep excision must have left some dysplastic cell behind. This is not a rare situation even when the margins appear negative under the microscope (5-10%). A repeat colonoscopy with biopsies and sampling the canal is a good idea. A second leep may be needed.