I have a nuvaring and i was trying to skip a period but it came anyways. what could i have done wrong? i kept it in for 4 weeks?

The nuvaring has time release hormones embedded within the plastic. They are typically tapering off in the 4th week. That is why you had a period. Directions indicate that the nuvaring should be taken out and left out for a week to allow for a period, then a new one inserted after that week is done. If you want to skip periods, try depo shots, or oral progesterone only contraceptives.