I take the active pills only then go to next pack to skip period. what do i do if miss 3 days of birth control?

Use a backup BC: The pills work by keeping a steady amount of hormone in your blood that prevents you from releasing eggs when due. If you skip 3 days and that hormone level drops, your body can decide to release an egg & that makes you at risk of conception during that interval. If you use backup BC like condoms for a week or two you should be fine.